A181537 Greatest k <= n such that 3^n + 3^k + 1 is prime or 0 if no such prime exists.

1, 2, 2, 4, 5, 6, 6, 2, 9, 6, 9, 0, 9, 12, 14, 16, 17, 15, 10, 18, 18, 13, 9, 22, 21, 18, 21, 16, 0, 30, 24, 11, 29, 9, 26, 32, 18, 15, 34, 39, 29, 37, 24, 27, 33, 31, 0, 30, 30, 15, 40, 43, 35, 54, 45, 42, 57, 51, 8, 60

Offset

1,2

Links

Pierre CAMI, Table of n, a(n) for n = 1..2000

Maple

A181537 := proc(n) local p, k; for k from n to 0 by -1 do p := 3^n+3^k+1 ; if isprime(p) then return k; end if; end do: return 0 ; end proc: # R. J. Mathar, Jan 30 2011

Mathematica

gk[n_]:=Module[{k=n, t=3^n+1}, While[!PrimeQ[t+3^k]&&k>0, k--]; k]; Array[ gk, 60] (* Harvey P. Dale, Jan 30 2019 *)

Crossrefs

Cf. A181530.

Sequence in context: A181523 A353855 A353847 * A130498 A263433 A147806

Adjacent sequences: A181534 A181535 A181536 * A181538 A181539 A181540

Keyword

nonn

Author

Pierre CAMI, Jan 29 2011

Status

approved