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 A264826 Primitive Eisenstein triples: (a,b,c) in lexicographic order such that a^2 + b^2 - a*b - c^2 = 0, a < b < c, and gcd(a, b) = 1. 2
 3, 7, 8, 5, 7, 8, 5, 19, 21, 7, 13, 15, 7, 37, 40, 8, 13, 15, 9, 61, 65, 11, 31, 35, 11, 91, 96, 13, 43, 48, 13, 127, 133, 15, 169, 176, 16, 19, 21, 16, 49, 55, 17, 73, 80, 17, 217, 225, 19, 91, 99, 19, 271, 280, 21, 331, 341, 23, 133, 143, 23, 397, 408 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The sides of a primitive 60-degree integer triangle. LINKS Colin Barker, Table of n, a(n) for n = 1..9999 Eric Weisstein's World of Mathematics, Pythagorean Triple Wikipedia, Eisenstein triple PROG (PARI) pt60(a) = {   my(L=List(), n=-3*a^2, f, g, b, c);   fordiv(n, f,     g=n\f;     if(f>g && (g+f)%2==0 && (f-g)%4==0,       b=(f-g)\4; c=((f+g)\2+a)\2;       if(c>0 && a

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Last modified August 21 05:32 EDT 2019. Contains 326162 sequences. (Running on oeis4.)