a(n) = Sum_{k>=0} (-1)^k*binomial(n, 5*k+2).

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =6a(5) =10a(6) =15a(7) =20a(8) =20a(9) =0a(10) =-75a(11) =-275a(12) =-725a(13) =-1625a(14) =-3250a(15) =-5875a(16) =-9500a(17) =-13125a(18) =-13125a(19) =0a(20) =47500a(21) =171875a(22) =450000a(23) =1006250a(24) =2012500a(25) =3640625a(26) =5890625a(27) =8140625a(28) =8140625a(29) =0