OFFSET
1,1
COMMENTS
J. L. Selfridge proved that a(8) > 100.
MATHEMATICA
lst = {}; p = 18; Do[p = Prime[n]; If[PrimeQ[2^p - 1], AppendTo[lst, p]], {n, p}]; Table[k = 1; While[i = 1; While[i <= n && PrimeQ[2^lst[[i]] + k], i++]; i <= n, k++]; k + 1, {n, Count[lst, _Integer]}]
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Arkadiusz Wesolowski, Jan 26 2012
STATUS
approved