OFFSET
1,2
COMMENTS
Even numbers of the form x^2 - xy + y^2.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
Even number 12 is a term because 12 = 2^2 + 2*2 + 2^2.
MATHEMATICA
Select[Range[0, 680, 2], Resolve@ Exists[{x, y}, Reduce[# == (x^2 - x y + y^2), {x, y}, Integers]] &] (* Michael De Vlieger, Mar 15 2016 *)
PROG
(PARI) x='x+O('x^800); p=eta(x)^3/eta(x^3); for(n=0, 799, if(polcoeff(p, n) != 0 && n % 2 == 0, print1(n, ", ")));
(PARI) list(lim)=my(v=List(), y, t); forstep(x=0, sqrtint(lim\3), 2, my(y=x, t); while((t=x^2+x*y+y^2)<=lim, listput(v, t); y+=2)); Set(v) \\ Charles R Greathouse IV, Jul 05 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Mar 14 2016
STATUS
approved