Number of subsets of {1,...,n} containing {a,a+4} for some a.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =8a(6) =28a(7) =74a(8) =175a(9) =377a(10) =799a(11) =1673a(12) =3471a(13) =7192a(14) =14784a(15) =30208a(16) =61440a(17) =124416a(18) =251328a(19) =506712a(20) =1020015a(21) =2051015a(22) =4119775a(23) =8268215a(24) =16582735a(25) =33239558a(26) =66599068a(27) =133392344a(28) =267099120a(29) =534709192