OFFSET
1,1
COMMENTS
Values of a^2 + b^2 such that (a^2 + b^2)^2 + a^2 + b^2 is not of the form x^2 + y^2 where a, b, x, y are nonzero integers.
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..10000
EXAMPLE
5 is a term because 5 = 1^2 + 2^2 and 5^2 + 5 = 30 is not a term of A000404.
MATHEMATICA
Select[Range@ 270, Length@ First@ # >= 1 && Last@ # == {} &[PowersRepresentations[#, 2, 2] /. {0, _} -> Nothing & /@ {#, # (# + 1)} &@ #] &] (* Michael De Vlieger, Apr 14 2016 *)
PROG
(PARI) isA000404(n) = {for( i=1, #n=factor(n)~%4, n[1, i]==3 && n[2, i]%2 && return); n && ( vecmin(n[1, ])==1 || (n[1, 1]==2 && n[2, 1]%2))}
for(n=1, 1e3, if(!isA000404(n*(n+1)) && isA000404(n), print1(n, ", ")));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Altug Alkan, Apr 14 2016
STATUS
approved