Number of n-element subsets of [n+8] having an even sum.

Terms

a(0) =1a(1) =4a(2) =20a(3) =85a(4) =255a(5) =636a(6) =1484a(7) =3235a(8) =6470a(9) =12120a(10) =21816a(11) =37854a(12) =63090a(13) =101640a(14) =159720a(15) =245322a(16) =367983a(17) =540540a(18) =780780a(19) =1110395a(20) =1554553a(21) =2145572a(22) =2925780a(23) =3945045a(24) =5260060a(25) =6941168a(26) =9076912a(27) =11769100a(28) =15131700a(29) =19302480