a(n) = 1*2*3*4*5 - 6*7*8*9*10 + 11*12*13*14*15 - ... + (up to n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =114a(6) =78a(7) =-216a(8) =-2904a(9) =-30120a(10) =-30109a(11) =-29988a(12) =-28404a(13) =-6096a(14) =330240a(15) =330224a(16) =329968a(17) =325344a(18) =237216a(19) =-1530240a(20) =-1530219a(21) =-1529778a(22) =-1519614a(23) =-1275216a(24) =4845360a(25) =4845334a(26) =4844658a(27) =4825704a(28) =4275336a(29) =-12255360