Number of subsets of { 1, ..., n } containing an A.P. of length 8.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =1a(9) =3a(10) =8a(11) =20a(12) =48a(13) =112a(14) =256a(15) =684a(16) =1696a(17) =3840a(18) =8575a(19) =18939a(20) =41452a(21) =90046a(22) =206952a(23) =466731a(24) =1037736a(25) =2233540a(26) =4782408a(27) =10194180a(28) =21638844a(29) =47278465