cp's OEIS Frontend

A159269 Least positive integer such that 2^m+3^n or 2^n+3^m is prime.

%I A159269 #6 Apr 06 2014 08:04:50
%S A159269 1,1,1,1,1,2,1,1,1,2,1,4,1,3,1,1,1,6,1,4,3,8,2,2,1,7,1,4,1,10,1,4,4,8,
%T A159269 15,6,1,2,3,8,3,3,2,6,3,11,6,2,5,4,18,4,12,6,26,1,4,2,9,6,4,10,18,1,4,
%U A159269 6,2,1,8,10,26,12,17,12,10,4,13,3,7,9,11,4,2,17,1,7,3,2,3,26,22,6,12,8,9
%N A159269 Least positive integer such that 2^m+3^n or 2^n+3^m is prime.
%C A159269 It seems that a(n)<=n for all n>0.
%F A159269 a(n) = min { A123359(n), A159266(n) }
%e A159269 a(0)=1 since 2^1+3^0=3 is prime.
%e A159269 a(1)=1 since 2^1+3^1=5 is prime.
%e A159269 a(2)=1 since 2^2+3^1=7, or 2^1+3^2=11, is prime. (Only one prime is required).
%e A159269 a(3)=1 since 2^3+3^1=11 and also 2^1+3^3=29, are prime.
%e A159269 a(4)=1 since 2^4+3^1=19 (and also 2^1+3^4=83) are prime.
%e A159269 a(5)=2 is the least integer m such that 2^5+3^m (=41) is prime and 2^m+3^5 is not prime until A159267(5)=4.
%o A159269 (PARI) A159269(n,m=0)=until( is/*pseudo*/prime(2^n+3^m++) || is/*pseudo*/prime(3^n+2^m),);m
%K A159269 nonn
%O A159269 0,6
%A A159269 _M. F. Hasler_, Apr 08 2009