OFFSET
1,2
COMMENTS
Terms (except 0) can be written as 4xy +- (x+y) for x > 0, y > 0. - Ron R Spencer, Jul 28 2016
Numbers k such that (4*k)!/(4*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 positive terms in the following triangular array:
2;
*, 6;
5, *, 12;
*, 11, *, 20;
8, *, 19, *, 30;
*, 16, *, 29, *, 42;
11, *, 26, *, 41, *, 56;
*, 21, *, 38, *, 55, *, 72;
14, *, 33, *, 52, *, 71, *, 90;
*, 26, *, 47, *, 68, *, 89, *, 110;
17, *, 40, *, 63, *, 86, *, 109, *, 132;
etc., where * marks the noninteger values of (2*h*k + k + h)/2 with h >= k >= 1. - Vincenzo Librandi, Jan 14 2013
MAPLE
for n from 0 to 100 do
if irem(factorial(4*n), 4*n+1) = 0 then print(n); end if;
end do: # Peter Bala, Jan 25 2017
MATHEMATICA
Select[Range[0, 200], ! PrimeQ[4 # + 1] &]
PROG
(Magma) [n: n in [0..220]| not IsPrime(4*n+1)]; // Vincenzo Librandi, Jan 28 2011
(PARI) is(n)=!isprime(4*n+1) \\ Charles R Greathouse IV, Jul 29 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Erich Friedman
STATUS
approved