a(n) = 5*4*3*2*1 - 10*9*8*7*6 + 15*14*13*12*11 - 20*19*18*17*16 + ... - (up to the n-th term).

Terms

a(0) =5a(1) =20a(2) =60a(3) =120a(4) =120a(5) =110a(6) =30a(7) =-600a(8) =-4920a(9) =-30120a(10) =-30105a(11) =-29910a(12) =-27390a(13) =2640a(14) =330240a(15) =330220a(16) =329860a(17) =323400a(18) =213960a(19) =-1530240a(20) =-1530215a(21) =-1529640a(22) =-1516440a(23) =-1226640a(24) =4845360a(25) =4845330a(26) =4844490a(27) =4821000a(28) =4187640a(29) =-12255360