Number of subsets of { 1, ..., n } containing an A.P. of length 7.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =3a(9) =8a(10) =20a(11) =48a(12) =112a(13) =300a(14) =752a(15) =1712a(16) =3839a(17) =8507a(18) =18668a(19) =43437a(20) =98919a(21) =221527a(22) =478718a(23) =1027994a(24) =2196398a(25) =4811804a(26) =10446823a(27) =22508560a(28) =48207309a(29) =101582640