cp's OEIS Frontend

A336773 a(n) is the least prime of the form 2^j*3^k + 1, j > 0, k > 0, j + k = n. a(n) = 0 if no such prime exists.

%I A336773 #9 Aug 30 2020 22:15:56
%S A336773 7,13,37,73,97,193,577,769,3457,10369,0,12289,629857,839809,147457,
%T A336773 995329,1990657,786433,5308417,120932353,14155777,28311553,0,
%U A336773 113246209,29386561537,3439853569,6879707137,1811939329,18345885697,3221225473,1253826625537,0,85691213438977
%N A336773 a(n) is the least prime of the form 2^j*3^k + 1, j > 0, k > 0, j + k = n. a(n) = 0 if no such prime exists.
%H A336773 Robert Israel, <a href="/A336773/b336773.txt">Table of n, a(n) for n = 2..2193</a>
%p A336773 f:= proc(n) local k,p;
%p A336773    for k from 1 to n-1 do
%p A336773      p:= 2^(n-k)*3^k+1;
%p A336773      if isprime(p) then return p fi
%p A336773    od;
%p A336773    0
%p A336773 end proc:
%p A336773 map(f, [$2..40]); # _Robert Israel_, Aug 30 2020
%o A336773 (PARI) for(n=2,34, my(pm=oo); for(j=1,n-1, my(k=n-j,p=2^j*3^k+1);if(isprime(p),pm=min(p,pm))); print1(if(pm==oo,0,pm),", "))
%Y A336773 Cf. A033845, A058383, A336772 (positions of 0).
%K A336773 nonn
%O A336773 2,1
%A A336773 _Hugo Pfoertner_, Aug 28 2020