Number of irregular primes less than 3^n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =3a(4) =9a(5) =48a(6) =131a(7) =334a(8) =880a(9) =2355a(10) =6341a(11) =17157a(12) =47620a(13) =132015a(14) =366790a(15) =1025835a(16) =2884928a(17) =8143498