a(1) = 1+2-3 = 0, a(2) = 4+5+6-7 = 8, a(3) = 8+9+10+11-12 = 26, a(4) = 13+14+15+16+17-18 = 57, ...

Terms

a(0) =0a(1) =8a(2) =26a(3) =57a(4) =104a(5) =170a(6) =258a(7) =371a(8) =512a(9) =684a(10) =890a(11) =1133a(12) =1416a(13) =1742a(14) =2114a(15) =2535a(16) =3008a(17) =3536a(18) =4122a(19) =4769a(20) =5480a(21) =6258a(22) =7106a(23) =8027a(24) =9024a(25) =10100a(26) =11258a(27) =12501a(28) =13832a(29) =15254