Number of prime powers p^k (k != 1) <= 10^n.

Terms

a(0) =1a(1) =4a(2) =11a(3) =26a(4) =52a(5) =109a(6) =237a(7) =556a(8) =1405a(9) =3690a(10) =10085a(11) =28157a(12) =80071a(13) =230568a(14) =670122a(15) =1962690a(16) =5782468a(17) =17124206a(18) =50930440a(19) =152043592a(20) =455389240a(21) =1367883344a(22) =4119448337a(23) =12434731102a(24) =37613760490a(25) =113995567275a(26) =346090346047