a(n) = 25*n*(n + 1)/2 + 1.

Terms

a(0) =1a(1) =26a(2) =76a(3) =151a(4) =251a(5) =376a(6) =526a(7) =701a(8) =901a(9) =1126a(10) =1376a(11) =1651a(12) =1951a(13) =2276a(14) =2626a(15) =3001a(16) =3401a(17) =3826a(18) =4276a(19) =4751a(20) =5251a(21) =5776a(22) =6326a(23) =6901a(24) =7501a(25) =8126a(26) =8776a(27) =9451a(28) =10151a(29) =10876