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%I #31 Mar 29 2023 04:53:06
%S 4,6,42,64,65,1017,3390,3894,8904,12976
%N Numbers k such that 43^k - 42 is prime.
%C Related to hyperperfect numbers of a certain form.
%C k = 1017 produces a 1662-digit number which is only a probable prime. Any additional terms are greater than 1500.
%C The next terms are > 3000. - _Vincenzo Librandi_, Sep 27 2012
%H J. S. McCranie, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/mccranie.html">A study of hyperperfect numbers</a>, J. Int. Seqs. Vol. 3 (2000) #P00.1.3.
%t Select[Range[1500], PrimeQ[43^# - 42] &] (* _Vincenzo Librandi_, Sep 27 2012 *)
%o (PARI) for(n=2,1500, if(isprime(43^n-42), print1(n,",")))
%K nonn,more
%O 1,1
%A _Jud McCranie_
%E a(6) from _Rick L. Shepherd_, Jun 21 2002
%E a(7)-a(8) from _Michael S. Branicky_, Aug 15 2021
%E a(9)-a(10) from _Michael S. Branicky_, Mar 28 2023
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