a(n) = n*(n+1)*(2*n+1)/3.

Terms

a(0) =0a(1) =2a(2) =10a(3) =28a(4) =60a(5) =110a(6) =182a(7) =280a(8) =408a(9) =570a(10) =770a(11) =1012a(12) =1300a(13) =1638a(14) =2030a(15) =2480a(16) =2992a(17) =3570a(18) =4218a(19) =4940a(20) =5740a(21) =6622a(22) =7590a(23) =8648a(24) =9800a(25) =11050a(26) =12402a(27) =13860a(28) =15428a(29) =17110