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.

7, 13, 37, 73, 97, 193, 577, 769, 3457, 10369, 0, 12289, 629857, 839809, 147457, 995329, 1990657, 786433, 5308417, 120932353, 14155777, 28311553, 0, 113246209, 29386561537, 3439853569, 6879707137, 1811939329, 18345885697, 3221225473, 1253826625537, 0, 85691213438977

Offset: 2

Author

Hugo Pfoertner, Aug 28 2020

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 2..2193

Crossrefs

Cf. A033845, A058383, A336772 (positions of 0).

Programs

Maple

f:= proc(n) local k,p;
   for k from 1 to n-1 do
     p:= 2^(n-k)*3^k+1;
     if isprime(p) then return p fi
   od;
   0
end proc:
map(f, [$2..40]); # Robert Israel, Aug 30 2020

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),", "))