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A153085
Numbers k such that 4*k + 5 is not prime.
2
1, 4, 5, 7, 10, 11, 13, 15, 16, 18, 19, 20, 22, 25, 28, 29, 30, 31, 32, 34, 35, 37, 39, 40, 41, 43, 45, 46, 49, 50, 51, 52, 53, 54, 55, 58, 60, 61, 62, 64, 65, 67, 70, 71, 73, 74, 75, 76, 79, 80, 81, 82, 84, 85, 88, 89, 90, 91, 93, 94, 95, 97, 100, 102, 103, 105, 106
OFFSET
1,2
COMMENTS
Let p=2n+1 be an odd number, then A140869(n,n) = (p^2-5)/4 = A028387(n-1).
One less than the associated entry in A045751: a(n) = A045751(n+1)-1. - R. J. Mathar, Jan 05 2011
LINKS
EXAMPLE
Triangle begins:
1;
*, 5;
4, *, 11;
*, 10, *, 19;
7, *, 18, *, 29;
*, 15, *, 28, *, 41;
where * mark the entries in A140869 which are non-integer if floor(.) is not applied there.
MATHEMATICA
Select[Range[200], !PrimeQ[4 # + 5] &] (* Vincenzo Librandi, Oct 15 2012 *)
PROG
(Magma) [n: n in [1..120] | not IsPrime(4*n + 5)]; // Vincenzo Librandi, Oct 15 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Dec 18 2008
STATUS
approved