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A203552
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a(n) = n*(5*n^2 - 3*n + 4) / 6.
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2
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0, 1, 6, 20, 48, 95, 166, 266, 400, 573, 790, 1056, 1376, 1755, 2198, 2710, 3296, 3961, 4710, 5548, 6480, 7511, 8646, 9890, 11248, 12725, 14326, 16056, 17920, 19923, 22070, 24366, 26816, 29425, 32198, 35140, 38256, 41551, 45030, 48698
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OFFSET
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0,3
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
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FORMULA
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a(n) = Sum_{k = 1..n} A(k-1, n-k) where A(i, j) = i^2 + i*j + j^2 + i + j + 1.
G.f.: x * (1 + 2*x + 2*x^2) / (1 - x)^4.
a( n) = -A203551(-n) for all n in Z.
a(n)-a(n-1) = A134238(n). - Bruno Berselli, Jan 03 2012
a(n) = 4*A000125(n) + 2*A000125(n+1) - A000125(n+3). - Ivan N. Ianakiev, Aug 21 2013
E.g.f.: x*(5*x^2 + 12*x + 6)*exp(x)/6. - G. C. Greubel, Aug 12 2018
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EXAMPLE
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G.f. = x + 6*x^2 + 20*x^3 + 48*x^4 + 95*x^5 + 166*x^6 + 266*x^7 + 400*x^8 + ...
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MATHEMATICA
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LinearRecurrence[{4, -6, 4, -1}, {0, 1, 6, 20}, 40] (* Vincenzo Librandi, Jan 07 2012 *)
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PROG
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(PARI) {a(n) = n * (5*n^2 - 3*n + 4) / 6};
(Magma) I:=[0, 1, 6, 20]; [n le 4 select I[n] else 4*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..50]]; // Vincenzo Librandi, Jan 07 2012
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CROSSREFS
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Cf. A203551.
Sequence in context: A005564 A011928 A055455 * A331754 A050768 A161438
Adjacent sequences: A203549 A203550 A203551 * A203553 A203554 A203555
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KEYWORD
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nonn,easy
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AUTHOR
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Michael Somos, Jan 02 2012
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STATUS
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approved
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