Number of subsets of { 1, ..., n } containing an A.P. of length 9.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =1a(10) =3a(11) =8a(12) =20a(13) =48a(14) =112a(15) =256a(16) =576a(17) =1488a(18) =3648a(19) =8208a(20) =18239a(21) =40123a(22) =87532a(23) =189630a(24) =408376a(25) =932127a(26) =2091911a(27) =4632601a(28) =9939498a(29) =21220735