

A093192


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


0



1, 1, 21, 1, 12, 16, 6, 112, 76, 195, 61, 21, 511, 909, 1689, 517, 640, 487, 13615, 12547, 382, 60456
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OFFSET

1,3


LINKS

Table of n, a(n) for n=1..22.


EXAMPLE

a(3) = 21: M(3) = 2^51 = 31; M(4) = 2^71 = 127; M(5) = 2^131 = 8191; 2*21*31*127*81911 = 1354414613, which is prime.


MATHEMATICA

spi[n_]:=Module[{k=2}, While[!PrimeQ[k*n1], k+=2]; k/2]; spi/@Times@@@ Partition[ Select[2^Range[5000]1, PrimeQ], 3, 1] (* The program generates the first 18 terms of the sequence. To generate more terms, increase the Range specification constant, but the program may take a long time to run. *) (* Harvey P. Dale, Dec 09 2018 *)


CROSSREFS

Sequence in context: A040456 A040457 A040458 * A040459 A040460 A040461
Adjacent sequences: A093189 A093190 A093191 * A093193 A093194 A093195


KEYWORD

nonn


AUTHOR

Ray G. Opao, Apr 21 2004


STATUS

approved



