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%I #6 Mar 05 2019 10:26:35
%S 0,0,5,22,91,286,863,2577,7717,23160,69939,209485,627826,1881554,
%T 5645226,16936048
%N Number of irregular primes less than or equal to the 3^n-th prime.
%C Limit_{n->inf.} a(n)/3^n = 1-e^(-1/2).
%t ip={ the list of irregular primes to 12 million }; Table[ Length[ Select[ip, # < Prime[3^n] &]], {n, 9}]
%Y Cf. A038833, A105458, A105462.
%K hard,nonn,more
%O 1,3
%A _Robert G. Wilson v_, Apr 07 2005
%E Terms corrected and a(10)-a(16) added by _Amiram Eldar_, Mar 05 2019