Alternating sum sigma(1)-sigma(2)+sigma(3)-sigma(4)+...+((-1)^(n+1))*sigma(n).

Terms

a(0) =1a(1) =-2a(2) =2a(3) =-5a(4) =1a(5) =-11a(6) =-3a(7) =-18a(8) =-5a(9) =-23a(10) =-11a(11) =-39a(12) =-25a(13) =-49a(14) =-25a(15) =-56a(16) =-38a(17) =-77a(18) =-57a(19) =-99a(20) =-67a(21) =-103a(22) =-79a(23) =-139a(24) =-108a(25) =-150a(26) =-110a(27) =-166a(28) =-136a(29) =-208