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%I #30 May 13 2018 04:38:34
%S 5,11,15,17,27,51,57,71,117,2073,6251,13671,14217,14627
%N Numbers k such that 2^(k-1) - k is prime.
%C a(15) > 200000. - _Giovanni Resta_, May 13 2018
%F a(n) = A099439(n) + 1 = A063791(n) + 2.
%e 5 is in the sequence, because 2^4 - 5 = 11 is prime.
%t Select[Range[6500], PrimeQ[2^(# - 1) - #] &] (* _Michael De Vlieger_, Apr 21 2018 *)
%o (PARI) forstep(n=1, 10^6, 2, if(ispseudoprime(2^(n-1)-n),print1(n,", "))); \\ _Joerg Arndt_, Apr 15 2018
%Y Cf. A063791, A099439.
%K nonn,more
%O 1,1
%A _Thomas Gajdek_, Dec 03 2017
%E Edited by _Joerg Arndt_, Apr 15 2018
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