a(n) = 1*2 - 3*4 + 5*6 - 7*8 + 9*10 - 11*12 + 13*14 - ... + (up to n).

Terms

a(0) =1a(1) =2a(2) =-1a(3) =-10a(4) =-5a(5) =20a(6) =13a(7) =-36a(8) =-27a(9) =54a(10) =43a(11) =-78a(12) =-65a(13) =104a(14) =89a(15) =-136a(16) =-119a(17) =170a(18) =151a(19) =-210a(20) =-189a(21) =252a(22) =229a(23) =-300a(24) =-275a(25) =350a(26) =323a(27) =-406a(28) =-377a(29) =464