Number of prime powers of prime numbers less than 10^n.

Terms

a(0) =3a(1) =7a(2) =18a(3) =40a(4) =88a(5) =208a(6) =513a(7) =1345a(8) =3605a(9) =9965a(10) =27984a(11) =79815a(12) =230184a(13) =669541a(14) =1961782a(15) =5781027a(16) =17121898a(17) =50926700a(18) =152037454a(19) =455379086a(20) =1367866472a(21) =4119420084a(22) =12434683582a(23) =37613680284a(24) =113995431428a(25) =346090115288