A153329 Numbers k such that 5*k + 1 is not prime.

0, 1, 3, 4, 5, 7, 9, 10, 11, 13, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 27, 28, 29, 31, 32, 33, 34, 35, 37, 39, 40, 41, 43, 44, 45, 46, 47, 49, 51, 52, 53, 55, 57, 58, 59, 60, 61, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 85, 87

Offset

1,3

Comments

Numbers k such that (5*k)!/(5*k + 1) is an integer. - Peter Bala, Jan 25 2017

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Example

Distribution of the even terms in the following triangular array:
   *;
   *,  *;
   4,  *,  *;
   *,  *,  *, 16;
   *,  *,  *,  *, 24;
   *,  *, 18,  *,  *,  *;
   *,  *,  *,  *,  *,  *,  *;
  10,  *,  *,  *,  *, 44,  *,  *;
   *,  *,  *, 34,  *,  *,  *,  *, 72;
   *,  *,  *,  *, 46,  *,  *,  *,  *, 88;
   *,  *, 32,  *,  *,  *,  *, 78,  *,  *,  *;
etc., where * marks the noninteger values of (4*h*k + 2*k + 2*h)/5 with h >= k >= 1. - Vincenzo Librandi, Jan 17 2013

Maple

for n from 0 to 100 do
if irem(factorial(5*n), 5*n+1) = 0 then print(n); end if;
end do: # Peter Bala, Jan 25 2017

Mathematica

Select[Range[0, 200], !PrimeQ[5*# + 1]&] (* Vincenzo Librandi, Jan 12 2013 *)

Prog

(Magma) [n: n in [0..150] | not IsPrime(5*n + 1)]; // Vincenzo Librandi, Jan 12 2013

Crossrefs

Cf. A024894, A014076, A153170, A045751, A095277, A153088, A153343.

Sequence in context: A335002 A276155 A273670 * A213637 A047251 A258932

Adjacent sequences: A153326 A153327 A153328 * A153330 A153331 A153332

Keyword

nonn,easy

Author

Vincenzo Librandi, Dec 23 2008

Extensions

Erroneous comment deleted by N. J. A. Sloane, Jun 23 2010

0 added by Arkadiusz Wesolowski, Aug 03 2011

Status

approved