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) =3a(4) =19a(5) =13a(6) =20a(7) =69a(8) =60a(9) =70a(10) =170a(11) =158a(12) =171a(13) =340a(14) =325a(15) =341a(16) =597a(17) =579a(18) =598a(19) =959a(20) =938a(21) =960a(22) =1444a(23) =1420a(24) =1445a(25) =2070a(26) =2043a(27) =2071a(28) =2855a(29) =2825