a(n) = n*(11*n - 1)/2.

Terms

a(0) =0a(1) =5a(2) =21a(3) =48a(4) =86a(5) =135a(6) =195a(7) =266a(8) =348a(9) =441a(10) =545a(11) =660a(12) =786a(13) =923a(14) =1071a(15) =1230a(16) =1400a(17) =1581a(18) =1773a(19) =1976a(20) =2190a(21) =2415a(22) =2651a(23) =2898a(24) =3156a(25) =3425a(26) =3705a(27) =3996a(28) =4298a(29) =4611