A117637 Least odd k such that (k*2^n)^2+k*2^n-1 is the first of twin primes with n>0.

1, 5, 1, 11, 9, 89, 25, 359, 187, 11, 145, 309, 559, 47, 115, 41, 87, 1169, 271, 41, 565, 1005, 1231, 245, 783, 185, 61, 431, 153, 1205, 423, 465, 2547, 1257, 891, 351, 25, 945, 937, 431, 453, 4221, 2763, 251, 783, 1761, 1381, 2493, 2125, 5241, 2871, 255, 4507

Offset

1,2

Links

Table of n, a(n) for n=1..53.

Example

(1*2^1)^2+1*2^1-1=5, 5 and 7 twin primes so k(1)=1
(1*2^2)^2+1*2^2-1=19 prime but 21 not prime
(3*2^2)^2+3*2^2-1=155 not prime
(5*2^2)^2+5*2^2-1=419, 419 and 421 twin primes so k(2)=5

Crossrefs

Sequence in context: A051853 A159074 A147414 * A332733 A132000 A132001

Adjacent sequences: A117634 A117635 A117636 * A117638 A117639 A117640

Keyword

nonn

Author

Pierre CAMI, Apr 09 2006

Status

approved