A344175 Primes of the form 2*3^a+5^b where 3^a+2*5^b is also prime, and a,b >= 1.

11, 23, 31, 43, 59, 179, 643, 2083, 13127, 15643, 15679, 42491, 1078507, 3579271, 19331563, 86094067, 6103515643, 8194271927, 783860159531, 15251196923099, 45753585300547, 411782264189423, 477025444560779, 1490116182146884843, 2390683931166760351, 186275633044228814171, 931322574615478517083

Offset

1,1

Comments

All terms == 3 (mod 4).

Links

Robert Israel, Table of n, a(n) for n = 1..55

Example

a(3) = 31 is a term because 31 = 2*3^1+5^2 and 3^1+2*5^2 = 53 are prime.

Maple

N:= 10^25: # for terms <= N
R:= NULL:
for a from 1 while 2*3^a < N do
  for b from 1 do
    x:= 2*3^a+5^b;
    if x > N then break fi;
    if isprime(x) and isprime(3^a + 2*5^b) then R:= R, x fi
od od:
sort([R]);

Crossrefs

Sequence in context: A110786 A059642 A090920 * A126330 A090506 A250215

Adjacent sequences: A344172 A344173 A344174 * A344176 A344177 A344178

Keyword

nonn

Author

J. M. Bergot and Robert Israel, May 11 2021

Status

approved