A340694 a(n) is the first prime p such that p*2^n+q*3^n is prime, where q is the prime following p.

2, 2, 5, 2, 5, 5, 7, 7, 5, 19, 7, 7, 5, 103, 7, 5, 7, 37, 5, 7, 31, 7, 211, 5, 197, 7, 17, 23, 7, 5, 5, 67, 17, 7, 7, 19, 127, 7, 7, 11, 7, 29, 79, 167, 79, 43, 89, 101, 17, 127, 89, 17, 137, 173, 71, 31, 73, 163, 67, 5, 11, 211, 31, 109, 67, 13, 7, 199, 97, 137, 109, 263, 107, 5, 101, 17, 283

Offset

0,1

Links

Robert Israel, Table of n, a(n) for n = 0..4400

Example

a(2) = 5 because 5*2^2+7*3^2 = 83 is prime, while 3*2^2+5*3^2 = 57 and 2*2^2+3*3^2 = 35 are not.

Maple

f:= proc(n) local p, q;
  q:= 2;
  do
    p:= q; q:= nextprime(q);
    until isprime(p*2^n+q*3^n);
  p
end proc:
map(f, [$0..100]);

Prog

(PARI) a(n) = my(p=2, q=nextprime(p+1)); while(! isprime(p*2^n+q*3^n), p=q; q=nextprime(p+1)); p; \\ Michel Marcus, Jan 21 2021

Crossrefs

Sequence in context: A171868 A292146 A334685 * A101910 A162784 A093660

Adjacent sequences: A340691 A340692 A340693 * A340695 A340696 A340697

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Jan 20 2021

Status

approved