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A181537 Greatest k <= n such that 3^n + 3^k + 1 is prime or 0 if no such prime exists. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A010848 A133937 A181523 * A130498 A263433 A147806

Adjacent sequences:  A181534 A181535 A181536 * A181538 A181539 A181540

KEYWORD

nonn

AUTHOR

Pierre CAMI, Jan 29 2011

STATUS

approved

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Last modified June 18 18:17 EDT 2021. Contains 345120 sequences. (Running on oeis4.)