Principal diagonal of the convolution array A213828.

Terms

a(0) =2a(1) =28a(2) =114a(3) =296a(4) =610a(5) =1092a(6) =1778a(7) =2704a(8) =3906a(9) =5420a(10) =7282a(11) =9528a(12) =12194a(13) =15316a(14) =18930a(15) =23072a(16) =27778a(17) =33084a(18) =39026a(19) =45640a(20) =52962a(21) =61028a(22) =69874a(23) =79536a(24) =90050a(25) =101452a(26) =113778a(27) =127064a(28) =141346a(29) =156660