Number of nontrivial prime powers p^k (k>1) less than 10^n.

Terms

a(0) =3a(1) =10a(2) =25a(3) =51a(4) =108a(5) =236a(6) =555a(7) =1404a(8) =3689a(9) =10084a(10) =28156a(11) =80070a(12) =230567a(13) =670121a(14) =1962689a(15) =5782467a(16) =17124205a(17) =50930439a(18) =152043591a(19) =455389239a(20) =1367883343a(21) =4119448336a(22) =12434731101a(23) =37613760489a(24) =113995567274a(25) =346090346046