a(n) = floor((n+1/n)^4).

Terms

a(0) =16a(1) =39a(2) =123a(3) =326a(4) =731a(5) =1446a(6) =2603a(7) =4358a(8) =6891a(9) =10406a(10) =15131a(11) =21318a(12) =29243a(13) =39206a(14) =51531a(15) =66566a(16) =84683a(17) =106278a(18) =131771a(19) =161606a(20) =196251a(21) =236198a(22) =281963a(23) =334086a(24) =393131a(25) =459686a(26) =534363a(27) =617798a(28) =710651a(29) =813606