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

1,1

Comments

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

Links

Table of n, a(n) for n=1..20.

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}]

Crossrefs

Cf. A004154, A078154, A078203, A078190.

Sequence in context: A247636 A361267 A070916 * A235324 A330373 A072599

Adjacent sequences: A078302 A078303 A078304 * A078306 A078307 A078308

Keyword

nonn,base,more

Author

Cino Hilliard, Dec 23 2002

Extensions

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

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

Status

approved