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A045751 Numbers k such that 4*k + 1 is not prime. 14
0, 2, 5, 6, 8, 11, 12, 14, 16, 17, 19, 20, 21, 23, 26, 29, 30, 31, 32, 33, 35, 36, 38, 40, 41, 42, 44, 46, 47, 50, 51, 52, 53, 54, 55, 56, 59, 61, 62, 63, 65, 66, 68, 71, 72, 74, 75, 76, 77, 80, 81, 82, 83, 85, 86, 89, 90, 91, 92, 94, 95, 96, 98, 101, 103, 104, 106, 107, 109 (list; graph; refs; listen; history; text; internal format)
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
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
Sequence in context: A024798 A108857 A132142 * A047267 A058591 A247062
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Erich Friedman
STATUS
approved

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Last modified March 19 07:21 EDT 2024. Contains 370955 sequences. (Running on oeis4.)