OFFSET
2,2
COMMENTS
Records: 1, 3, 4, 5, 6, 7, 9, 11, 12, 16, 21, 22, 25, 26, ..., - Robert G. Wilson v, Mar 20 2018
When k >= 2*n-1, k! is a multiple of (2*n-1); then 2*n - 1 + k! is a multiple of (2*n-1) so it cannot be prime. - Michel Marcus, May 20 2018
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 2..1500
EXAMPLE
a(7)=3 because there are 3 primes of the form k!+13, i.e., 19 = 3!+13, 37 = 4!+13, 733 = 6!+13.
MATHEMATICA
f[n_] := Block[{c = 0, k = 1, od = 2n -1}, While[k < od, If[PrimeQ[k! + od], c++]; k++]; c]; f@# & /@ Range[2, 100] (* Robert G. Wilson v, Mar 18 2018 *)
PROG
(PARI) a(n) = sum(k=2, 2*n-1, isprime(2*n - 1 + k!)); \\ Michel Marcus, May 19 2018
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
G. L. Honaker, Jr., Mar 18 2018
EXTENSIONS
More terms from Robert G. Wilson v, Mar 18 2018
STATUS
approved