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%I #23 Apr 15 2024 12:10:12
%S 0,1,4,5,8,10,25,49,76,128,175,238,550,796,1219,2012,2846,11336,21296,
%T 49808,74318,236891,608989,1715905,5112847
%N Numbers n such that 8*10^n-1 is prime.
%C Also numbers n such that 7*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/79999.htm#prime">Prime numbers of the form 799...99</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Do[ If[ PrimeQ[ 7*10^n + (10^n-1)], Print[n]], {n, 0, 3000}]
%o (PARI) is(n)=ispseudoprime(8*10^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017
%K hard,nonn,more,changed
%O 1,3
%A _Robert G. Wilson v_, Aug 11 2000
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
%E a(22)-a(23) from Kamada data by _Robert Price_, Oct 19 2014
%E a(24)-a(25) from Kamada data by _Tyler Busby_, Apr 15 2024
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