Diagonal of triangular spiral in A051682.

Terms

a(0) =1a(1) =12a(2) =32a(3) =61a(4) =99a(5) =146a(6) =202a(7) =267a(8) =341a(9) =424a(10) =516a(11) =617a(12) =727a(13) =846a(14) =974a(15) =1111a(16) =1257a(17) =1412a(18) =1576a(19) =1749a(20) =1931a(21) =2122a(22) =2322a(23) =2531a(24) =2749a(25) =2976a(26) =3212a(27) =3457a(28) =3711a(29) =3974