Sum along upward diagonal of Pascal triangle up to (but not including) center.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =4a(5) =5a(6) =6a(7) =17a(8) =23a(9) =30a(10) =73a(11) =103a(12) =141a(13) =314a(14) =455a(15) =643a(16) =1350a(17) =1993a(18) =2881a(19) =5798a(20) =8679a(21) =12761a(22) =24872a(23) =37633a(24) =56070a(25) =106573a(26) =162643a(27) =244906a(28) =456169a(29) =701075