A100014 Least a(n) such that a(n)*2^n*(2^n-1)+1 is prime.

1, 1, 2, 1, 6, 3, 5, 12, 3, 5, 8, 6, 5, 3, 18, 8, 41, 5, 11, 14, 66, 8, 2, 9, 18, 8, 21, 12, 30, 16, 6, 1, 6, 8, 33, 2, 53, 23, 2, 5, 21, 15, 6, 12, 20, 5, 5, 28, 53, 80, 11, 53, 9, 5, 56, 2, 120, 5, 23, 16, 9, 8, 5, 9, 24, 25, 62, 131, 41, 51, 12, 3, 99, 56, 2, 37, 155, 3, 23, 55, 29, 9, 2, 33

Offset: 1

Author

Pierre CAMI, Nov 18 2004

Keywords

• easy
• nonn

Comments

Numbers n such that a(n)=2 are found in A006598. - Michel Marcus, Mar 07 2013

Examples

			1*2^5*(2^5-1)+1=993=3*331
2*2^5*(2^5-1)+1=1985=5*397
3*2^5*(2^5-1)+1=2977=13*229
4*2^5*(2^5-1)+1=3969=3*1323
5*2^5*(2^5-1)+1=4961=11*451
6*2^5*(2^5-1)+1=5953 prime so a(5)=6
		

Programs

PARI

a(n) = {k = 1; while (! isprime(k*2^n*(2^n-1) + 1), k++); return (k);} \\ Michel Marcus, Mar 07 2013