Number of subsets of {1..n} whose elements have the same smallest prime factor.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =7a(6) =11a(7) =12a(8) =20a(9) =22a(10) =38a(11) =39a(12) =71a(13) =72a(14) =136a(15) =140a(16) =268a(17) =269a(18) =525a(19) =526a(20) =1038a(21) =1046a(22) =2070a(23) =2071a(24) =4119a(25) =4121a(26) =8217a(27) =8233a(28) =16425a(29) =16426