Principal diagonal of the convolution array A213819.

Terms

a(0) =2a(1) =18a(2) =60a(3) =140a(4) =270a(5) =462a(6) =728a(7) =1080a(8) =1530a(9) =2090a(10) =2772a(11) =3588a(12) =4550a(13) =5670a(14) =6960a(15) =8432a(16) =10098a(17) =11970a(18) =14060a(19) =16380a(20) =18942a(21) =21758a(22) =24840a(23) =28200a(24) =31850a(25) =35802a(26) =40068a(27) =44660a(28) =49590a(29) =54870