Number of isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n.

Terms

a(0) =0a(1) =3a(2) =15a(3) =35a(4) =69a(5) =106a(6) =162a(7) =222a(8) =300a(9) =382a(10) =486a(11) =587a(12) =715a(13) =840a(14) =997a(15) =1147a(16) =1313a(17) =1491a(18) =1700a(19) =1890a(20) =2129a(21) =2341a(22) =2598a(23) =2842a(24) =3126a(25) =3394a(26) =3711a(27) =3995a(28) =4341a(29) =4641