

A172995


Numbers k such that (3^k + 7)/2 is prime.


2



1, 3, 7, 75, 191, 395, 891, 2935, 3855, 59887, 125447
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OFFSET

1,2


COMMENTS

Naturally these numbers are odd since 3^(2*k) + 7 = (8+1)^k + 7 == 0 (mod 8).  Bruno Berselli, Oct 08 2012
For n <= 9, (3^a(n) + 7)/2 has been proved prime using PARI's ECPP; a(10) corresponds to a BPSW PRP. a(11) > 10^5.  Lucas A. Brown, Feb 10 2021


LINKS



MATHEMATICA



PROG



CROSSREFS



KEYWORD

nonn,hard,more,changed


AUTHOR



EXTENSIONS



STATUS

approved



