a(n) = n^2*(n^2 + 15)/4.

Terms

a(0) =0a(1) =4a(2) =19a(3) =54a(4) =124a(5) =250a(6) =459a(7) =784a(8) =1264a(9) =1944a(10) =2875a(11) =4114a(12) =5724a(13) =7774a(14) =10339a(15) =13500a(16) =17344a(17) =21964a(18) =27459a(19) =33934a(20) =41500a(21) =50274a(22) =60379a(23) =71944a(24) =85104a(25) =100000a(26) =116779a(27) =135594a(28) =156604a(29) =179974