Number of primes <= 5^n.

Terms

a(0) =0a(1) =3a(2) =9a(3) =30a(4) =114a(5) =445a(6) =1821a(7) =7671a(8) =33118a(9) =145713a(10) =650133a(11) =2934858a(12) =13375865a(13) =61444585a(14) =284140656a(15) =1321453490a(16) =6175961983a(17) =28988040005a(18) =136575061279a(19) =645620925545