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 - ... + (up to n).

A319550

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 - ... + (up to n).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =720a(6) =5040a(7) =40320a(8) =362880a(9) =362870a(10) =362770a(11) =361560a(12) =345720a(13) =122640a(14) =-3240720a(15) =-57294720a(16) =-979816320a(17) =-17642862720a(18) =-17642862701a(19) =-17642862340a(20) =-17642854740a(21) =-17642687160a(22) =-17638824840a(23) =-17545953600a(24) =-15220134720a(25) =45348065280

External references