Number of subsets of { 1, ..., n } containing an A.P. of length 6.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =3a(8) =8a(9) =20a(10) =48a(11) =136a(12) =344a(13) =788a(14) =1775a(15) =3947a(16) =9373a(17) =21533a(18) =48327a(19) =104676a(20) =224997a(21) =496490a(22) =1082575a(23) =2334984a(24) =4997364a(25) =10532236a(26) =22568064a(27) =48062489a(28) =101796210a(29) =214545469