A259534 a(n) = -1 + 2 * product_{i=0..n} A093179(i), where A093179(i) is the smallest prime factor of 2^(2^i) + 1.

5, 29, 509, 131069, 8589934589, 5506148072189, 1509659159988837629, 90050548615896750734368618889875709, 111565998552535226317138856424609779410946920431869, 270528914968139650436266764640655805238384653911572627709

Offset: 0

Author

Arkadiusz Wesolowski, Jul 02 2015

Keywords

• nonn

Comments

For any k >= 1, numbers of the form (k*a(n) + k - 1)*2^m - 1 are composite for all m < 2^(n+1).

Many terms are in common with A006285 (de Polignac numbers).

Crossrefs

Cf. A006285, A093179.

Programs

PARI

a(n) = - 1 + 2 * prod(k=0, n, factor(2^(2^k)+1)[1,1]); \\ Michel Marcus, Jul 04 2015