cp's OEIS Frontend

A090649 Numbers k such that 9^k + 2 is prime.

%I A090649 #32 Jun 07 2021 01:12:30
%S A090649 0,1,2,4,5,7,12,13,18,49,55,63,193,247,610,929,2173,3479,5494,11158,
%T A090649 16754,30920,47752,50702,53725,68122,89214,180804
%N A090649 Numbers k such that 9^k + 2 is prime.
%C A090649 All terms are the exact halves of the even terms in A051783. - _Alexander Adamchuk_, Mar 02 2008
%C A090649 a(29) > 2*10^5. - _Robert Price_, Aug 18 2014
%H A090649 Henri Lifchitz and Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=3%5En%2B2&amp;action=Search">PRP Records</a>.
%e A090649 9^13 + 2 = 2541865828331 is prime, so 13 is a term.
%t A090649 Do[ If[ PrimeQ[9^n + 2], Print[n]], {n, 1, 2250}] (* _Robert G. Wilson v_, Feb 06 2004 *)
%o A090649 (PARI) for(i=0,700,if(isprime(9^i+2),print(i)))
%Y A090649 Cf. A051783 (3^k + 2 is prime), A087885 (5^k + 2 is prime).
%K A090649 nonn,more,hard
%O A090649 1,3
%A A090649 Herman H. Rosenfeld (herm3(AT)pacbell.net), Feb 02 2004
%E A090649 More terms from mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 04 2004
%E A090649 Further terms from _Robert G. Wilson v_ and _Ray Chandler_, Feb 06 2004
%E A090649 a(20) - a(22) found by _Henri Lifchitz_, a(23) found by Wojciech Florek. - _Jason Earls_, Feb 25 2008
%E A090649 a(24)-a(27) from A051783 by _Ray Chandler_, Aug 06 2011
%E A090649 a(28) from _Robert Price_, Aug 18 2014
%E A090649 Removal of erroneous term (97715) by _Robert Price_, Aug 19 2014