a(n) = n*(n+1)*(20*n-17)/6.

Terms

a(0) =0a(1) =1a(2) =23a(3) =86a(4) =210a(5) =415a(6) =721a(7) =1148a(8) =1716a(9) =2445a(10) =3355a(11) =4466a(12) =5798a(13) =7371a(14) =9205a(15) =11320a(16) =13736a(17) =16473a(18) =19551a(19) =22990a(20) =26810a(21) =31031a(22) =35673a(23) =40756a(24) =46300a(25) =52325a(26) =58851a(27) =65898a(28) =73486a(29) =81635