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A093481 Least k such that (2n + k) + 1 and (2n*k) + 1 are both primes. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 5 00:21 EST 2021. Contains 349530 sequences. (Running on oeis4.)