A142884 a(n) = 1 if a(n-1) is prime, else a(n) = a(n-2)+a(n-3); starting with a(0) = 0, a(1) = a(2) = 1.

0, 1, 1, 1, 2, 1, 3, 1, 4, 4, 5, 1, 9, 6, 10, 15, 16, 25, 31, 1, 56, 32, 57, 88, 89, 1, 177, 90, 178, 267, 268, 445, 535, 713, 980, 1248, 1693, 1, 2941, 1694, 2942, 4635, 4636, 7577, 1, 12213, 7578, 12214, 19791, 19792, 32005, 39583, 51797, 1, 91380, 51798, 91381, 1

Offset

0,5

Comments

Original title: "Prime finding sequence recursion where the primes are sums of two integers".

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Example

15 + 16 = 31,
32 + 57 = 89,
713 + 980 = 1693,
19792 + 32005 = 51797,
237122034 + 314186695 = 551308729.

Mathematica

Clear[a, n]; a[0] = 0; a[1] = 1; a[2] = 1; a[n_] := a[n] = If[PrimeQ[a[n - 1]], 1, a[n - 2] + a[n - 3]]; Table[a[n], {n, 0, 100}]

Crossrefs

Sequence in context: A278575 A333879 A175126 * A347028 A325365 A177687

Adjacent sequences: A142881 A142882 A142883 * A142885 A142886 A142887

Keyword

nonn,less

Author

Roger L. Bagula, Sep 28 2008

Extensions

Edited by M. F. Hasler, Feb 09 2014

Status

approved