a(n) = (n+1)*(n^2+n+2)/2; g.f.: (1 + 2*x^2) / (1 - x)^4.

Terms

a(0) =1a(1) =4a(2) =12a(3) =28a(4) =55a(5) =96a(6) =154a(7) =232a(8) =333a(9) =460a(10) =616a(11) =804a(12) =1027a(13) =1288a(14) =1590a(15) =1936a(16) =2329a(17) =2772a(18) =3268a(19) =3820a(20) =4431a(21) =5104a(22) =5842a(23) =6648a(24) =7525a(25) =8476a(26) =9504a(27) =10612a(28) =11803a(29) =13080