Twice second pentagonal numbers.

Terms

a(0) =0a(1) =4a(2) =14a(3) =30a(4) =52a(5) =80a(6) =114a(7) =154a(8) =200a(9) =252a(10) =310a(11) =374a(12) =444a(13) =520a(14) =602a(15) =690a(16) =784a(17) =884a(18) =990a(19) =1102a(20) =1220a(21) =1344a(22) =1474a(23) =1610a(24) =1752a(25) =1900a(26) =2054a(27) =2214a(28) =2380a(29) =2552