a(n) = T(4,n), array T given by A048472.

Terms

a(0) =1a(1) =6a(2) =21a(3) =61a(4) =161a(5) =401a(6) =961a(7) =2241a(8) =5121a(9) =11521a(10) =25601a(11) =56321a(12) =122881a(13) =266241a(14) =573441a(15) =1228801a(16) =2621441a(17) =5570561a(18) =11796481a(19) =24903681a(20) =52428801a(21) =110100481a(22) =230686721a(23) =482344961a(24) =1006632961a(25) =2097152001a(26) =4362076161a(27) =9059696641a(28) =18790481921a(29) =38923141121