A092527 If M(n) is the n-th Mersenne prime, then a(n) is the smallest positive integer such that 2*a(n)*M(n)*M(n+1)-1 is prime.

1, 1, 1, 12, 1, 25, 3, 13, 7, 153, 43, 423, 52, 916, 136, 1111, 1270, 442, 2737, 975

Offset

1,4

Comments

a(21) > 4200. - Robert G. Wilson v

a(21) > 12000, a(22)=6669, a(23) > 10000, a(24)=5970. - Ray G. Opao, Apr 15 2004

Links

Table of n, a(n) for n=1..20.

Example

a(4) = 12: 2(12)(2^7-1)(2^13-1)-1 = 24(127)(8191)-1 = 24966167, which is prime.

Mathematica

p = { (* the list of Mersenne exponents in A000043 *) }; f[n_] := Block[{k = 1, q = 2^p[[n]] - 1, r = 2^p[[n + 1]] - 1}, While[ !PrimeQ[2k*q*r - 1], k++ ]; k]; Do[ Print[ f[n]], {n, 25}] (* Robert G. Wilson v, Apr 10 2004 *)

Crossrefs

Sequence in context: A040155 A036185 A013619 * A085840 A276966 A277799

Adjacent sequences: A092524 A092525 A092526 * A092528 A092529 A092530

Keyword

nonn

Author

Ray G. Opao, Apr 08 2004

Status

approved