a(n) = 1*2*3*4*5*6*7*8*9*10 - 11*12*13*14*15*16*17*18*19*20 + 21*22*23*24*25*26*27*28*29*30 - ... + (up to n).

A319551

a(n) = 1*2*3*4*5*6*7*8*9*10 - 11*12*13*14*15*16*17*18*19*20 + 21*22*23*24*25*26*27*28*29*30 - ... + (up to n).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =720a(6) =5040a(7) =40320a(8) =362880a(9) =3628800a(10) =3628789a(11) =3628668a(12) =3627084a(13) =3604776a(14) =3268440a(15) =-2136960a(16) =-94389120a(17) =-1760693760a(18) =-33518499840a(19) =-670438944000a(20) =-670438943979a(21) =-670438943538a(22) =-670438933374a(23) =-670438688976a(24) =-670432568400a(25) =-670273178400

External references