Partial sums of A051880.

Terms

a(0) =1a(1) =16a(2) =91a(3) =336a(4) =966a(5) =2352a(6) =5082a(7) =10032a(8) =18447a(9) =32032a(10) =53053a(11) =84448a(12) =129948a(13) =194208a(14) =282948a(15) =403104a(16) =562989a(17) =772464a(18) =1043119a(19) =1388464a(20) =1824130a(21) =2368080a(22) =3040830a(23) =3865680a(24) =4868955a(25) =6080256a(26) =7532721a(27) =9263296