A078305 Numbers k such that A004154(k) - 1 is prime.

3, 4, 5, 6, 7, 13, 14, 19, 20, 28, 37, 99, 100, 108, 141, 304, 442, 682, 3641, 4076

Offset: 1

Author

Cino Hilliard, Dec 23 2002

Keywords

• nonn
• base
• more

Comments

Some of the larger entries may only correspond to probable primes.

Crossrefs

Cf. A004154, A078154, A078203, A078190.

Programs

Mathematica

f[n_] := n!/10^Sum[ Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ f[n] - 1], Print[n]], {n, 1, 750}]

Extensions

Extended by Robert G. Wilson v and Jason Earls, Dec 24 2002

a(19)-a(20) from Michael S. Branicky, Jul 23 2023