Staggered diagonal of triangular spiral in A051682.

Terms

a(0) =0a(1) =6a(2) =21a(3) =45a(4) =78a(5) =120a(6) =171a(7) =231a(8) =300a(9) =378a(10) =465a(11) =561a(12) =666a(13) =780a(14) =903a(15) =1035a(16) =1176a(17) =1326a(18) =1485a(19) =1653a(20) =1830a(21) =2016a(22) =2211a(23) =2415a(24) =2628a(25) =2850a(26) =3081a(27) =3321a(28) =3570a(29) =3828