0,3

This sequence represents the expected saturation of a binary search tree (or BST) on n nodes times the number of binary search trees on n nodes, or alternatively, the sum of the saturation of all binary search trees on n nodes. - Marko Riedel, Jan 24 2002

1->12, 2->123, 3->1234 etc. starting with 1, gives A007001: 1, 12, 12123, 12123121231234... summing the digits gives this sequence. - Miklos Kristof, Nov 05 2002

a(n-1) = number of n-th generation vertices in the tree of sequences with unit increase labeled by 2 (cf. Zoran Sunik reference). - Benoit Cloitre, Oct 07 2003

With offset 1, number of permutations beginning with 12 and avoiding 32-1.

Number of lattice paths from (0,0) to (n,n) with steps E=(1,0) and N=(0,1) which touch but do not cross the line x-y=1. - Herbert Kociemba, May 24 2004

a(n)=number of Dyck (n+1)-paths that start with UU. For example, a(2)=3 counts UUUDDD, UUDUDD, UUDDUD. - David Callan, Dec 08 2004

a(n)=number of Dyck (n+2)-paths that start with UUDU. For example, a(2)=3 counts UUDUDDUD, UUDUDUDD, UUDUUDDD. - David Scambler, Feb 14 2011

Hankel transform is (0,-1,-1,0,1,1,0,-1,-1, 0...). Hankel transform of a(n+1) is (1,0,-1,-1,0,1,1,0,-1,-1,0...). - Paul Barry, Feb 08 2008

Starting with offset 1 = row sums of triangle A154558. - Gary W. Adamson, Jan 11 2009

Starting with offset 1 equals INVERT transform of A014137, partial sums of the Catalan numbers: (1, 2, 4, 9, 23,...). - Gary W. Adamson, May 15 2009

With offset 1, a(n) is the binomial transform of the shortened Motzkin numbers: 1, 2, 4, 9, 21, 51, 127, 323....(A001006). - Aoife Hennessy (aoife.hennessy(AT)gmail.com), Sep 07 2009

The Catalan sequence convolved with its shifted variant, e.g. a(5) = 90 = (1, 1, 2, 5, 14) dot (42, 14, 5, 2, 1) = (42 + 14 + 10 + 10 + 14 ) = 90. - Gary W. Adamson, Nov 22 2011

a(n+2) = A214292(2*n+3,n). - Reinhard Zumkeller, Jul 12 2012

With offset 3, a(n) is the number of permutations on {1,2,...,n} that are 123-avoiding, i.e., do not contain a three term monotone subsequence, for which the first ascent is at positions (3,4); see Connolly link. There it is shown in general that the k-th Catalan Convolution is the number of 123-avoiding permutations for which the first ascent is at (k, k+1). (For n=k, the first ascent is defined to be at positions (k,k+1) if the permutation is the decreasing permutation with no ascents.) - Anant Godbole, Jan 17 2014

With offset 3, a(n)=number of permutations on {1,2,...,n} that are 123-avoiding and for which the integer n is in the 3rd spot; see Connolly link. For example, there are 297 123-avoiding permutations on n=9 at which the element 9 is in the third spot. - Anant Godbole, Jan 17 2014

S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 196).

P. de la Harpe, Topics in Geometric Group Theory, Univ. Chicago Press, 2000, p. 11, coefficients of P_3(z).

Kim, Ki Hang; Rogers, Douglas G.; Roush, Fred W. Similarity relations and semiorders. Proceedings of the Tenth Southeastern Conference on Combinatorics, Graph Theory and Computing (Florida Atlantic Univ., Boca Raton, Fla., 1979), pp. 577-594, Congress. Numer., XXIII-XXIV, Utilitas Math., Winnipeg, Man., 1979. MR0561081 (81i:05013)

C. Krishnamachary and M. Bheemasena Rao, Determinants whose elements are Eulerian, prepared Bernoullian and other numbers, J. Indian Math. Soc., 14 (1922), 55-62, 122-138 and 143-146.

A. Papoulis, A new method of inversion of the Laplace transform, Quart. Applied Math. 14 (1956), 405ff.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n=0..100

Marco Abrate, Stefano Barbero, Umberto Cerruti, Nadir Murru, Colored compositions, Invert operator and elegant compositions with the "black tie", Discrete Math. 335 (2014), 1-7. MR3248794

J.-L. Baril, Classical sequences revisited with permutations avoiding dotted pattern, Electronic Journal of Combinatorics, 18 (2011), #P178.

Paul Barry, A Catalan Transform and Related Transformations on Integer Sequences, Journal of Integer Sequences, Vol. 8 (2005), Article 05.4.5.

D. Callan, A recursive bijective approach to counting permutations..., arXiv:math/0211380, Nov 25 2002.

S. Connolly, Z. Gabor and A. Godbole, The location of the first ascent in a 123-avoiding permutation, arXiv:1401.2691 [math.CO]

Dennis E. Davenport, Lara K. Pudwell, Louis W. Shapiro, Leon C. Woodson, The Boundary of Ordered Trees, Journal of Integer Sequences, Vol. 18 (2015), Article 15.5.8.

Filippo Disanto, Some Statistics on the Hypercubes of Catalan Permutations, Journal of Integer Sequences, Vol. 18 (2015), Article 15.2.2.

Filippo Disanto and Thomas Wiehe, Some instances of a sub-permutation problem on pattern avoiding permutations, arXiv preprint arXiv:1210.6908, 2012.

F. Disanto and T. Wiehe, On the sub-permutations of pattern avoiding permutations, Discrete Math., 337 (2014), 127-141.

N. S. S. Gu, N. Y. Li and T. Mansour, 2-Binary trees: bijections and related issues, Discr. Math., 308 (2008), 1209-1221.

R. K. Guy, Catwalks, Sandsteps and Pascal Pyramids, J. Integer Seqs., Vol. 3 (2000), #00.1.6

Guo-Niu Han, Enumeration of Standard Puzzles [broken link]

Guo-Niu Han, Enumeration of Standard Puzzles [Cached copy]

V. E. Hoggatt, Jr. and M. Bicknell, Catalan and related sequences arising from inverses of Pascal's triangle matrices, Fib. Quart., 14 (1976), 395-405.

S. Kitaev, Generalized pattern avoidance with additional restrictions, Sem. Lothar. Combinat. B48e (2003).

S. Kitaev and T. Mansour, Simultaneous avoidance of generalized patterns, arXiv:math.co/0205182

C. Krishnamachary and M. Bheemasena Rao, Determinants whose elements are Eulerian, prepared Bernoullian and other numbers, J. Indian Math. Soc., 14 (1922), 55-62, 122-138 and 143-146. [Annotated scanned copy]

A. Papoulis, A new method of inversion of the Laplace transform, Quart. Appl. Math 14 (1957), 405-414. [Annotated scan of selected pages]

J.-B. Priez, A. Virmaux, Non-commutative Frobenius characteristic of generalized parking functions: Application to enumeration, arXiv:1411.4161 [math.CO], 2014-2015.

Jocelyn Quaintance and Harris Kwong, A combinatorial interpretation of the Catalan and Bell number difference tables, Integers, 13 (2013), #A29.

J. Riordan, The distribution of crossings of chords joining pairs of 2n points on a circle, Math. Comp., 29 (1975), 215-222.

Zoran Sunik, Self describing sequences and the Catalan family tree, Elect. J. Combin., 10 (No. 1, 2003).

S. J. Tedford, Combinatorial interpretations of convolutions of the Catalan numbers, Integers 11 (2011) #A3

G.f.: x*(c(x))^3 = (-1+(1-x)*c(x))/x, c(x) = g.f. for Catalan numbers. Also a(n)=3*n*Catalan(n)/(n+2). - Wolfdieter Lang

For n>1, a(n) = 3a(n-1) + Sum[a(k)*a(n-k-2), k=1,...,n-3]. - John W. Layman, Dec 13 2002; proved by Michael Somos, Jul 05 2003

G.f. is A(x) = C(x)*(1-x)/x-1/x = x(1+x*C(x)^2)*C(x)^2 where C(x) is g.f. for Catalan numbers, A000108.

G.f. satisfies x^2*A(x)^2+(3*x-1)*A(x)+x = 0.

Series reversion of g.f. A(x) is -A(-x). - Michael Somos, Jan 21 2004

a(n+1) = sum(i+j+k=n, C(i)C(j)C(k)) with i, j, k>=0 and where C(k) denotes the k-th Catalan number. - Benoit Cloitre, Nov 09 2003

An inverse Chebyshev transform of x^2. - Paul Barry, Oct 13 2004

The sequence is 0, 0, 1, 0, 3, 0, 9, 0, ...with zeros restored. Second binomial transform of (-1)^n*A005322(n). The g.f. is transformed to x^2 under the Chebyshev transformation A(x)->(1/(1+x^2))A(x/(1+x^2)). For a sequence b(n), this corresponds to taking sum{k=0..floor(n/2), C(n-k, k)(-1)^k*b(n-2k)}, or sum{k=0..n, C((n+k)/2, k)*b(k)*(-1)^((n-k)/2)*(1+(-1)^(n-k))/2}. - Paul Barry, Oct 13 2004

G.f.: (c(x^2)*(1-x^2)-1)/x^2, c(x) the g.f. of A000108; a(n)=sum{k=0..n, (k+1)*C(n, (n-k)/2)*(-1)^k*(C(2,k)-2*C(1,k)+C(0, k))*(1+(-1)^(n-k))/(n+k+2)}. - Paul Barry, Oct 13 2004

a(n) = Catalan(n+1) - Catalan(n) = sum{k=0..n, binomial(n,k)*2^(n-k)*(-1)^(k+1)*binomial(k,floor((k-1)/2))}. - Paul Barry, Feb 16 2006

E.g.f.: exp(2*x)*(Bessel_I(1,2x)-Bessel_I(2,2*x)). - Paul Barry, Jun 04 2007

a(n) = (1/pi)*int(x^n*(x-1)*sqrt(x*(4-x))/(2*x),x,0,4). - Paul Barry, Feb 08 2008

For n>1, a(n+1) = 2*(2n+1)*(n+1)*a(n)/((n+3)*n). - Sean A. Irvine, Dec 09 2009

Let A be the Toeplitz matrix of order n defined by: A[i,i-1]=-1, A[i,j] = Catalan(j-i), (i<=j), and A[i,j] = 0, otherwise. Then, for n>=2, a(n-1)=(-1)^(n-2)*coeff(charpoly(A,x),x^2). - Milan Janjic, Jul 08 2010

a(n) = sum of top row terms of M^(n-1), M = an infinite square production matrix as follows:

2, 1, 0, 0, 0, 0,...

1, 1, 1, 0, 0, 0,...

1, 1, 1, 1, 0, 0,...

1, 1, 1, 1, 1, 0,...

1, 1, 1, 1, 1, 1,...

...

- Gary W. Adamson, Jul 14 2011

E.g.f.: exp(2*x)*(BesselI(2,2*x)) = Q(0) - 1 where Q(k)= 1 - 2*x/(k + 1 - 3*((k+1)^2)/((k^2) + 8*k + 9 - (k+2)*((k+3)^2)*(2*k+3)/((k+3)*(2*k+3) - 3*(k+1)/Q(k+1)))); (continued fraction). - Sergei N. Gladkovskii, Dec 05 2011

a(n) = -binomial(2*n,n)/(n+1)*hypergeom([-1,n+1/2],[n+2],4). - Peter Luschny, Aug 15 2012

a(n) = sum(i=0..n-1, C(i)*C(n-i)), where C(i) denotes the i-th Catalan number. - Dmitry Kruchinin, Mar 02 2013

a(n) = binomial(2*n-1, n) - binomial(2*n-1, n-3). - Johannes W. Meijer, Jul 31 2013

A000245 := n -> 3*binomial(2*n, n-1)/(n+2); seq(A000245(n), n=0..27);

Table[3(2n)!/((n+2)!(n-1)!), {n, 0, 30}] (* or *) Table[3*Binomial[2n, n-1]/(n+2), {n, 0, 30}] (* or *) Differences[CatalanNumber[Range[0, 31]]] (* Harvey P. Dale, Jul 13 2011 *)

(PARI) a(n)=if(n<1, 0, 3*(2*n)!/(n+2)!/(n-1)!)

(Sage) [catalan_number(i+1)-catalan_number(i) for i in xrange(0, 28)]# Zerinvary Lajos, May 17 2009

(Sage)

def A000245_list(n) :

    D = [0]*(n+1); D[1] = 1

    b = False; h = 1; R = []

    for i in range(2*n-1) :

        if b :

            for k in range(h, 0, -1) : D[k] += D[k-1]

            h += 1; R.append(D[2])

        else :

            for k in range(1, h, 1) : D[k] += D[k+1]

        b = not b

    return R

A000245_list(29) # Peter Luschny, Jun 03 2012

First differences of Catalan numbers A000108.

T(n, n+3) for n=0, 1, 2, ..., array T as in A047072.

Also a diagonal of A059365 and of A009766.

Cf. A099364

A diagonal of any of the essentially equivalent arrays A009766, A030237, A033184, A059365, A099039, A106566, A130020, A047072.

Cf. A000108, A002057, A000344, A003517, A000588, A003518, A003519, A001392.

Cf. A154558, A014137

Sequence in context: A094826 A033190 A071724 * A143739 A189940 A047047

Adjacent sequences:  A000242 A000243 A000244 * A000246 A000247 A000248

nonn,easy,nice,changed

N. J. A. Sloane

I changed the description and added an initial 0, to make this coincide with the first differences of the Catalan numbers A000108. Some of the other lines will need to be changed as a result. - N. J. A. Sloane, Oct 31 2003

approved