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A153329 Numbers k such that 5*k + 1 is not prime. 7
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Numbers k such that (5*k)!/(5*k + 1) is an integer. - Peter Bala, Jan 25 2017
LINKS
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
Sequence in context: A335002 A276155 A273670 * A213637 A047251 A258932
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

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Last modified May 29 14:43 EDT 2024. Contains 372952 sequences. (Running on oeis4.)