cp's OEIS Frontend

A219040 Numbers k such that 3^k + 20 is prime.

%I A219040 #27 Nov 12 2023 08:47:03
%S A219040 1,2,3,4,5,7,8,10,11,14,44,55,68,71,80,123,158,213,220,272,668,725,
%T A219040 885,1132,1677,2056,2618,3130,3986,6027,8660,11582,12278,14054,62956,
%U A219040 103431,120434,123890,181407
%N A219040 Numbers k such that 3^k + 20 is prime.
%C A219040 a(40) > 2*10^5. - _Robert Price_, Oct 20 2013
%e A219040 3^3 + 20 = 47 (prime), so 3 is in the sequence.
%t A219040 Do[If[PrimeQ[3^n + 20], Print[n]], {n, 10000}]
%o A219040 (PARI) is(n)=isprime(3^n+20) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A219040 Cf. Sequences of numbers k such that 3^k + m is prime:
%Y A219040   (m = 2) A051783, (m = -2) A014224, (m = 4) A058958, (m = -4) A058959,
%Y A219040   (m = 8) A217136, (m = -8) A217135, (m = 10) A217137, (m = -10) A217347,
%Y A219040   (m = 14) A219035, (m = -14) A219038, (m = 16) A205647, (m = -16) A219039,
%Y A219040   (m = 20) A219040, (m = -20) A219041, (m = 22) A219042, (m = -22) A219043,
%Y A219040   (m = 26) A219044, (m = -26) A219045, (m = 28) A219046, (m = -28) A219047,
%Y A219040   (m = 32) A219048, (m = -32) A219049, (m = 34) A219050, (m = -34) A219051. Note that if m is a multiple of 3, 3^k + m is also a multiple of 3 (for k greater than 0), and as such isn't prime.
%K A219040 nonn,more
%O A219040 1,2
%A A219040 _Nicolas M. Perrault_, Nov 10 2012
%E A219040 a(32)-a(39) from _Robert Price_, Oct 20 2013