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%I #24 Apr 18 2023 10:20:47
%S 0,1,6,11,23,297,474,1121,2531,3573,5437,5919
%N Numbers k such that 8*10^(2*k) + 8*10^k + 1 are prime.
%e 17 is prime. ==> a(1) = 0.
%e 881 is prime. ==> a(2) = 1.
%e 80801 = 7^2 * 17 * 97.
%e 8008001 = 47 * 170383.
%e 800080001 = 7 * 23 * 103 * 48247.
%e 80000800001 = 71 * 1126771831.
%e 8000008000001 is prime. ==> a(3) = 6.
%o (PARI) for(k=0, 1e3, if(ispseudoprime(8*100^k+8*10^k+1), print1(k", ")))
%o (Python)
%o from sympy import isprime
%o def afind(limit, startk=0):
%o for k in range(startk, limit+1):
%o if isprime(8*100**k + 8*10**k + 1): print(k, end=", ")
%o afind(500) # _Michael S. Branicky_, Dec 12 2021
%Y Cf. A309739.
%K nonn,more
%O 1,3
%A _Seiichi Manyama_, Aug 15 2019
%E a(11) from _Michael S. Branicky_, Dec 12 2021
%E a(12) from _Michael S. Branicky_, Apr 16 2023
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