a(n) = n + (n-1)^2 + (n+1)^2.

Terms

a(0) =2a(1) =5a(2) =12a(3) =23a(4) =38a(5) =57a(6) =80a(7) =107a(8) =138a(9) =173a(10) =212a(11) =255a(12) =302a(13) =353a(14) =408a(15) =467a(16) =530a(17) =597a(18) =668a(19) =743a(20) =822a(21) =905a(22) =992a(23) =1083a(24) =1178a(25) =1277a(26) =1380a(27) =1487a(28) =1598a(29) =1713