Number of subsets of {1,...,n} containing {a,a+2,a+4} for some a.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =4a(6) =15a(7) =37a(8) =87a(9) =200a(10) =448a(11) =992a(12) =2160a(13) =4628a(14) =9823a(15) =20699a(16) =43335a(17) =90246a(18) =187068a(19) =386192a(20) =794560a(21) =1629944a(22) =3334975a(23) =6808073a(24) =13870191a(25) =28207552a(26) =57274368a(27) =116129280a(28) =235165632a(29) =475678200