a(n) = 250*n - 70.

Terms

a(0) =-70a(1) =180a(2) =430a(3) =680a(4) =930a(5) =1180a(6) =1430a(7) =1680a(8) =1930a(9) =2180a(10) =2430a(11) =2680a(12) =2930a(13) =3180a(14) =3430a(15) =3680a(16) =3930a(17) =4180a(18) =4430a(19) =4680a(20) =4930a(21) =5180a(22) =5430a(23) =5680a(24) =5930a(25) =6180a(26) =6430a(27) =6680a(28) =6930a(29) =7180