a(n) = Sum_{i=0..n} T(i,n-i), array T as in A048149.

Terms

a(0) =1a(1) =6a(2) =16a(3) =38a(4) =69a(5) =120a(6) =190a(7) =276a(8) =387a(9) =542a(10) =714a(11) =924a(12) =1161a(13) =1456a(14) =1794a(15) =2174a(16) =2597a(17) =3084a(18) =3620a(19) =4230a(20) =4891a(21) =5610a(22) =6418a(23) =7292a(24) =8213a(25) =9248a(26) =10366a(27) =11566a(28) =12827a(29) =14200