OFFSET
1,3
COMMENTS
Inspired by intersection of nice and core sequences. Initial Mersenne numbers of the form x^2 + xy + y^2 are 0, 1, 3, 7, 31, 63, 127, 511, 8191, 16383.
EXAMPLE
a(4) = 3 because 2^3 - 1 = 1^2 + 1*2 + 2^2 = 7.
a(5) = 5 because 2^5 - 1 = 1^2 + 1*5 + 5^2 = 31.
PROG
(PARI) is(n)=#bnfisintnorm(bnfinit(z^2+z+1), 2^n-1);
for(n=0, 200, if(n==0 || is(n), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Nov 18 2015
STATUS
approved