7-dimensional centered tetrahedral numbers.

Terms

a(0) =1a(1) =9a(2) =45a(3) =165a(4) =495a(5) =1287a(6) =3003a(7) =6435a(8) =12869a(9) =24301a(10) =43713a(11) =75417a(12) =125475a(13) =202203a(14) =316767a(15) =483879a(16) =722601a(17) =1057265a(18) =1518517a(19) =2144493a(20) =2982135a(21) =4088655a(22) =5533155a(23) =7398411a(24) =9782829a(25) =12802581a(26) =16593929