OFFSET
1,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..2000
EXAMPLE
a(2)=7: (7^2 + 1)/2 = 25, which is not prime, so 7 is in the sequence.
(9^2 + 1)/2 = 41, which is prime, so 9 is not in the sequence.
MATHEMATICA
a={}; For[i=1, i<100, i=i+2, If[PrimeQ[(i^2+1)/2], 0, AppendTo[a, i]]]Print[a]
Select[Range[1, 201, 2], !PrimeQ[(#^2+1)/2]&] (* Harvey P. Dale, Jan 07 2016 *)
PROG
(Magma) [ n: n in [1..200 by 2] | not IsPrime((n^2+1) div 2) ];
(PARI) isok(n) = (n%2) && !isprime((n^2 + 1)/2); \\ Michel Marcus, Nov 23 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Meiburg, Aug 21 2010
EXTENSIONS
More terms from Vincenzo Librandi, Nov 18 2010
Example clarified by Harvey P. Dale, Jan 07 2016
STATUS
approved