a(n) = 49*n^2 - 7.

Terms

a(0) =42a(1) =189a(2) =434a(3) =777a(4) =1218a(5) =1757a(6) =2394a(7) =3129a(8) =3962a(9) =4893a(10) =5922a(11) =7049a(12) =8274a(13) =9597a(14) =11018a(15) =12537a(16) =14154a(17) =15869a(18) =17682a(19) =19593a(20) =21602a(21) =23709a(22) =25914a(23) =28217a(24) =30618a(25) =33117a(26) =35714a(27) =38409a(28) =41202a(29) =44093