a(n) = binomial(n,0) - binomial(n,2) + binomial(n,4).

Terms

a(0) =1a(1) =1a(2) =0a(3) =-2a(4) =-4a(5) =-4a(6) =1a(7) =15a(8) =43a(9) =91a(10) =166a(11) =276a(12) =430a(13) =638a(14) =911a(15) =1261a(16) =1701a(17) =2245a(18) =2908a(19) =3706a(20) =4656a(21) =5776a(22) =7085a(23) =8603a(24) =10351a(25) =12351a(26) =14626a(27) =17200a(28) =20098a(29) =23346