a(n)=60*sum(1<=i<=j<=k<=n,i*j^2/k).

Terms

a(0) =0a(1) =60a(2) =450a(3) =1790a(4) =5195a(5) =12419a(6) =25999a(7) =49399a(8) =87154a(9) =145014a(10) =230088a(11) =350988a(12) =517973a(13) =743093a(14) =1040333a(15) =1425757a(16) =1917652a(17) =2536672a(18) =3305982a(19) =4251402a(20) =5401551a(21) =6787991a(22) =8445371a(23) =10411571a(24) =12727846a(25) =15438970a(26) =18593380a(27) =22243320a(28) =26444985a(29) =31258665