A095967 Numbers k such that R3(d) * 2^k + 1 is prime, where R3() = A002277 and d is the number of decimal digits of 2^k.

1, 2, 6, 9, 20, 46, 58, 64, 69, 110, 158, 178, 186, 268, 424, 624, 641, 1236, 1593, 2264, 2870, 5797, 7518, 7688, 9300, 16238

Offset

1,2

Comments

a(1) through a(25) have been proved to be prime with WinPFGW. a(25) has 5600 digits. No more terms up to 12800.

Results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019

Links

Table of n, a(n) for n=1..26.

Example

a(4) = 9 is a term because 2^9 = 512 has 3 digits and 333 * 2^9 + 1 = 170497, a prime.

Crossrefs

Cf. A002277, A095306.

Sequence in context: A265016 A279897 A336131 * A316429 A337639 A387123

Adjacent sequences: A095964 A095965 A095966 * A095968 A095969 A095970

Keyword

nonn,base,hard,more

Author

Jason Earls, Jul 15 2004

Extensions

a(26) from Michael S. Branicky, Feb 08 2026

Status

approved