Number of n-digit numbers that have exactly 3 divisors.

Terms

a(0) =2a(1) =2a(2) =7a(3) =14a(4) =40a(5) =103a(6) =278a(7) =783a(8) =2172a(9) =6191a(10) =17701a(11) =51205a(12) =149149a(13) =436932a(14) =1287378a(15) =3809498a(16) =11321211a(17) =33764868a(18) =101029398a(19) =303175579a(20) =912147300a(21) =2750855002a(22) =8313825647a(23) =25176031558a(24) =76375623757a(25) =232082001064a(26) =706304629714