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%I #10 Apr 11 2020 06:05:17
%S 11,19,27,31,41,47,53,67,73,87,91,97,109,129,151,153,187,203,209,217,
%T 231,243,273,283,311,323,373,389,423,433,447,451,467,481,539,549,581,
%U 583,591,607,621,623,637,643,657,659,663,669,673,677,691,693,699,753
%N Exactly 4 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime.
%H Daniel Starodubtsev, <a href="/A032694/b032694.txt">Table of n, a(n) for n = 1..10000</a>
%e If a(n) = 109 then we find '1'109, '3'109, '7'109 and '9'109 to be primes.
%o (Python)
%o from sympy import isprime
%o print([i for i in range(800) if [isprime(int(j + str(i))) for j in '123456789'].count(True) == 4]) # _Daniel Starodubtsev_, Apr 11 2020
%K nonn,base
%O 1,1
%A _Patrick De Geest_, May 15 1998
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