Number of n-digit numbers that have exactly 5 divisors.

Terms

a(0) =0a(1) =2a(2) =1a(3) =1a(4) =3a(5) =4a(6) =5a(7) =9a(8) =15a(9) =25a(10) =37a(11) =66a(12) =107a(13) =171a(14) =293a(15) =490a(16) =810a(17) =1362a(18) =2302a(19) =3889a(20) =6552a(21) =11149a(22) =18950a(23) =32255a(24) =55053a(25) =94096a(26) =161036a(27) =275896a(28) =473709a(29) =813669