Number of isosceles triangles on a centered hexagonal grid of size n.

Terms

a(0) =0a(1) =20a(2) =252a(3) =1296a(4) =4232a(5) =10668a(6) =22956a(7) =43832a(8) =77160a(9) =126972a(10) =198176a(11) =296976a(12) =429252a(13) =602876a(14) =825552a(15) =1106376a(16) =1454192a(17) =1879956a(18) =2397024a(19) =3014312a(20) =3747564a(21) =4609476