Principal diagonal of the convolution array A213847.

Terms

a(0) =3a(1) =36a(2) =131a(3) =320a(4) =635a(5) =1108a(6) =1771a(7) =2656a(8) =3795a(9) =5220a(10) =6963a(11) =9056a(12) =11531a(13) =14420a(14) =17755a(15) =21568a(16) =25891a(17) =30756a(18) =36195a(19) =42240a(20) =48923a(21) =56276a(22) =64331a(23) =73120a(24) =82675a(25) =93028a(26) =104211a(27) =116256a(28) =129195a(29) =143060