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%I #43 Sep 30 2020 03:54:57
%S 0,5,29,186,1345,10544,86537,733409,6363181,56196113,503193256,
%T 4555800188,41621368073,383118399785,3549047966156,33056584174789,
%U 309353882390965,2907021742443974,27417323062119920,259423936749134301,2461813897281353729,23422580231698331834
%N Number of primes <= R_n where R_n is 11...111 with n 1's.
%H David Baugh, <a href="/A234317/b234317.txt">Table of n, a(n) for n = 1..26</a> (terms n = 16..26 found with Kim Walisch's primecount program).
%F a(n) = A000720(R_n) = A000720(A002275(n)) where R_n is 11...111 with n 1's.
%e There are 1345 primes less than or equal to 11111. Thus a(5) = 1345.
%t PrimePi/@Table[FromDigits[PadRight[{},n,1]],{n,15}] (* The program will take a long time to run *) (* _Harvey P. Dale_, Jan 21 2015 *)
%o (Python)
%o import sympy
%o from sympy import primepi
%o for n in range(1,50):
%o ..print(primepi((10**n-1)/9),end=', ')
%o (PARI) a(n)=primepi(10^n\9) \\ _Charles R Greathouse IV_, Apr 30 2014
%Y Cf. A000720, A002275.
%K nonn,less
%O 1,2
%A _Derek Orr_, Dec 23 2013
%E a(14)-a(15) from _Hiroaki Yamanouchi_, Sep 27 2014
%E a(16)-a(22) from _David Baugh_, Sep 29 2020
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