A120621 Least positive k such that !n + k is prime, where !n is left factorial.

2, 1, 1, 1, 1, 3, 3, 3, 9, 3, 7, 9, 7, 13, 49, 27, 9, 37, 19, 33, 7, 93, 103, 9, 73, 27, 13, 27, 165, 49, 39, 93, 97, 27, 37, 39, 135, 7, 193, 249, 39, 103, 13, 33, 213, 129, 33, 13, 39, 115, 187, 19, 7, 387, 19, 489, 303, 63, 33, 235, 297, 495, 657, 465, 235, 193, 369, 129

Offset: 0

Author

Jason Earls, Aug 17 2006

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A003422, A033932 (with n! instead of !n).

Programs

Mathematica

a[n_] := Module[{k = 1, lf = Sum[i!, {i, 0, n - 1}]}, While[!PrimeQ[lf + k], k++]; k]; Array[a, 100, 0] (* Amiram Eldar, Dec 24 2019 *)