A289856 Primes of the form k!2 - 256, where k!2 is the double factorial number (A006882).

10139, 2026769, 13749310319, 213458046676619, 191898783962510369, 157952079428395476360490147277859119, 29215606371473169285018060091249259296619, 2395415678676082004163677716234578672981800778515369

Offset: 1

Author

Robert Price, Jul 13 2017

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..12
• Henri and Renaud Lifchitz, PRP Records.Search for n!2-256.
• Joe McLean, Interesting Sources of Probable Primes.
• OpenPFGW Project, Primality Tester.

Crossrefs

Cf. A006882, A265114.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n<1, 1, n*MultiFactorial[n-k, k]];
Select[Table[MultiFactorial[i, 2] - 256, {i, 8, 100}], PrimeQ[#]&]

Formula

a(n) = A006882(A265114(n)) - 256. - Elmo R. Oliveira, Apr 14 2025