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

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

Twice A093312.

Sequence in context: A094048 A179073 A087665 * A132629 A288161 A302454

Adjacent sequences: A093478 A093479 A093480 * A093482 A093483 A093484

Keyword

nonn

Author

Amarnath Murthy, Apr 14 2004

Extensions

Edited, corrected and extended by Robert G. Wilson v, Apr 24 2004

Status

approved