a(n)=12*sum(1<=i<=j<=k<=n,i*j/k).

Terms

a(0) =0a(1) =12a(2) =54a(3) =154a(4) =349a(5) =685a(6) =1217a(7) =2009a(8) =3134a(9) =4674a(10) =6720a(11) =9372a(12) =12739a(13) =16939a(14) =22099a(15) =28355a(16) =35852a(17) =44744a(18) =55194a(19) =67374a(20) =81465a(21) =97657a(22) =116149a(23) =137149a(24) =160874a(25) =187550a(26) =217412a(27) =250704a(28) =287679a(29) =328599