a(n) = (n^4 + 20*n^3 + 125*n^2 + 250*n + 24)/12.

Terms

a(0) =2a(1) =35a(2) =100a(3) =210a(4) =380a(5) =627a(6) =970a(7) =1430a(8) =2030a(9) =2795a(10) =3752a(11) =4930a(12) =6360a(13) =8075a(14) =10110a(15) =12502a(16) =15290a(17) =18515a(18) =22220a(19) =26450a(20) =31252a(21) =36675a(22) =42770a(23) =49590a(24) =57190a(25) =65627a(26) =74960a(27) =85250a(28) =96560a(29) =108955