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Number of irregular primes less than or equal to the 2^n-th prime.
2

%I #14 Mar 09 2019 05:13:21

%S 0,0,0,1,6,16,47,96,206,406,823,1626,3244,6454,12798,25715,51779,

%T 103315,206649,412883,825395,1650179,3299610,6600347,13201348,26403834

%N Number of irregular primes less than or equal to the 2^n-th prime.

%C Lim_{n->inf.} a(n)/2^n = 1 - e^(-1/2).

%t ip={ the list of irregular primes to 12 million }; Table[ Length[ Select[ip, # <= Prime[2^n] &]], {n, 19}]

%Y Cf. A000928, A033844, A105456, A105460.

%K hard,nonn,more

%O 1,5

%A _Robert G. Wilson v_, Apr 07 2005

%E Data corrected and a(20)-a(26) added by _Amiram Eldar_, Mar 05 2019