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A095306
Numbers n such that r(k) * 2^n + 1 is prime, where r() = A002275 the repunits and k is the number of decimal digits of 2^n.
0
1, 2, 5, 12, 19, 107, 117, 159, 217, 517, 868, 1412, 1636, 4051, 5965, 9128
OFFSET
1,2
COMMENTS
a(1) through a(16) have been proved to be prime with WinPFGW. a(16) has 5495 digits. No more terms up to 11700.
Results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019
EXAMPLE
a(5)=19 because 111111 * 2^19 + 1 = 58254163969, a prime.
CROSSREFS
Sequence in context: A116728 A276478 A333558 * A356649 A258602 A327065
KEYWORD
more,nonn,base
AUTHOR
Jason Earls, Jul 13 2004
STATUS
approved