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A055496
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a(1) = 2; a(n) is smallest prime > 2*a(n-1).
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33
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2, 5, 11, 23, 47, 97, 197, 397, 797, 1597, 3203, 6421, 12853, 25717, 51437, 102877, 205759, 411527, 823117, 1646237, 3292489, 6584983, 13169977, 26339969, 52679969, 105359939, 210719881, 421439783, 842879579, 1685759167, 3371518343
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OFFSET
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1,1
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COMMENTS
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It appears that lim_{n->infinity} a(n)/2^n exists and is approximately 1.569985585.... - Franklin T. Adams-Watters, Nov 11 2011
This is a B_2 sequence. - Thomas Ordowski, Sep 23 2014 See the link.
Conjecture: lim_{n->infinity} a(n)/A006992(n) = 5.1648264... - Thomas Ordowski, Apr 05 2015
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LINKS
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Zak Seidov and Michael De Vlieger, Table of n, a(n) for n = 1..1000 (First 100 terms from Zak Seidov)
V. Shevelev, Ramanujan and Labos primes, their generalizations, and classifications of primes, J. Integer Seq. 15 (2012), #12.5.4.
Eric Weisstein's World of Mathematics, B_2-Sequence.
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FORMULA
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a(n+1) = A060264(a(n)). - Peter Munn, Oct 23 2017
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MAPLE
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A055496 := proc(n) option remember; if n=1 then 2 else nextprime(2*A055496(n-1)); fi; end;
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MATHEMATICA
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NextPrim[n_Integer] := Block[ {k = n + 1}, While[ !PrimeQ[k], k++ ]; Return[k]]; a[1] = 2; a[n_] := NextPrim[ 2*a[n - 1]]; Table[ a[n], {n, 1, 31} ]
a[1]=2; a[n_]:=a[n]=Prime[PrimePi[2*a[n-1]]+1]; Table[a[n], {n, 40}] (* Zak Seidov, Feb 16 2006 *)
NestList[ NextPrime[2*# ]&, 2, 100] (* Zak Seidov, Jul 28 2009 *)
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PROG
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(PARI) print1(a=2); for(n=2, 20, print1(", ", a=nextprime(a+a))) \\ Charles R Greathouse IV, Jul 19 2011
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CROSSREFS
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Cf. A006992, A060264, A163963.
Values of a(n)-2*a(n-1) in A163469. - Zak Seidov, Jul 28 2009
Cf. A065545 (with a(1)=3). - Zak Seidov, Feb 04 2016
Row 1 of A229608.
Sequence in context: A081973 A357292 A334276 * A105120 A084403 A261201
Adjacent sequences: A055493 A055494 A055495 * A055497 A055498 A055499
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Jul 07 2000
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EXTENSIONS
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Mathematica updated by Jean-François Alcover, Jun 19 2013
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STATUS
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approved
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