Triangular numbers of the form k^2 + k + 1.

Terms

a(0) =1a(1) =3a(2) =21a(3) =91a(4) =703a(5) =3081a(6) =23871a(7) =104653a(8) =810901a(9) =3555111a(10) =27546753a(11) =120769111a(12) =935778691a(13) =4102594653a(14) =31788928731a(15) =139367449081