a(n) = (-1)^(n+1) * n*(n-1)*(n-4)*(n+1)/12.

Terms

a(0) =1a(1) =-2a(2) =0a(3) =10a(4) =-35a(5) =84a(6) =-168a(7) =300a(8) =-495a(9) =770a(10) =-1144a(11) =1638a(12) =-2275a(13) =3080a(14) =-4080a(15) =5304a(16) =-6783a(17) =8550a(18) =-10640a(19) =13090a(20) =-15939a(21) =19228a(22) =-23000a(23) =27300a(24) =-32175a(25) =37674a(26) =-43848a(27) =50750a(28) =-58435a(29) =66960