0 followed by the sum of (1),(2), (3,4),(5,6), (7,8,9),(10,11,12) from the natural numbers.

Terms

a(0) =0a(1) =1a(2) =2a(3) =7a(4) =11a(5) =24a(6) =33a(7) =58a(8) =74a(9) =115a(10) =140a(11) =201a(12) =237a(13) =322a(14) =371a(15) =484a(16) =548a(17) =693a(18) =774a(19) =955a(20) =1055a(21) =1276a(22) =1397a(23) =1662a(24) =1806a(25) =2119a(26) =2288a(27) =2653a(28) =2849a(29) =3270