A093481 - OEIS

A093481

Least k such that (2n + k) + 1 and (2n*k) + 1 are both primes.

2, 18, 6, 2, 6, 6, 2, 6, 4, 2, 18, 4, 2, 12, 6, 8, 12, 16, 20, 6, 10, 2, 6, 4, 2, 6, 24, 2, 30, 10, 26, 18, 6, 2, 36, 6, 8, 6, 4, 8, 66, 4, 2, 24, 6, 14, 12, 6, 2, 6, 4, 32, 30, 4, 26, 18, 34, 50, 30, 10, 8, 12, 52, 2, 18, 16, 2, 60, 10, 32, 6, 4, 2, 30, 12, 14, 24, 6, 14, 30, 10, 14, 6, 4, 8

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OFFSET

1,1

COMMENTS

For n>1 a(n) is even and also if a(n) = m then a(m/2) = 2n.

LINKS

Table of n, a(n) for n=1..85.

EXAMPLE

a(4) = 2, 8 + 2 + 1 = 11 and 8*2 + 1 = 17 are both prime.

MATHEMATICA

f[n_] := Block[{k = 1}, While[ !PrimeQ[2n + k + 1] || ! PrimeQ[2n*k + 1], k++ ]; k]; Table[ f[n], {n, 85}] (* Robert G. Wilson v, Apr 24 2004 *)

CROSSREFS