a(n)=T(n+1,n), array T given by A048225.

Terms

a(0) =1a(1) =3a(2) =8a(3) =17a(4) =27a(5) =39a(6) =52a(7) =67a(8) =85a(9) =106a(10) =129a(11) =158a(12) =190a(13) =224a(14) =261a(15) =302a(16) =345a(17) =390a(18) =437a(19) =485a(20) =538a(21) =594a(22) =651a(23) =711a(24) =774a(25) =839a(26) =908a(27) =980a(28) =1054a(29) =1129