A182414 Least k such that 4^n - 2^k - 1 is prime with n-1 < k < 2*n or 0 if no solution.

0, 2, 4, 4, 5, 7, 8, 11, 9, 10, 16, 13, 0, 23, 16, 23, 28, 18, 20, 23, 22, 30, 0, 29, 26, 47, 28, 42, 0, 33, 41, 0, 42, 48, 37, 45, 53, 38, 57, 46, 0, 70, 66, 52, 45, 0, 49, 81, 58, 50, 74, 86, 0, 57, 56, 94, 57, 0, 64, 80, 96, 64, 72, 97, 77, 87, 0, 104, 77

Offset

1,2

Comments

Less than 10 % of a(n)=0.

Links

Pierre CAMI, Table of n, a(n) for n = 1..4560

Example

n=2:2^(2*n)-2^1-1=13 prime but n-1=1=k so k not > n-1.
2^(2*n)-2^2-1=11 prime k=2 k>n-1 so a(2)=2.

Mathematica

Table[k = n; While[k < 2*n && ! PrimeQ[4^n - 2^k - 1], k++]; If[k == 2*n, k = 0]; k, {n, 100}] (* T. D. Noe, May 02 2012 *)

Crossrefs

Cf. A182413.

Sequence in context: A339769 A147534 A118001 * A256984 A111138 A349462

Adjacent sequences: A182411 A182412 A182413 * A182415 A182416 A182417

Keyword

nonn

Author

Pierre CAMI, Apr 28 2012

Status

approved