A277124 Numbers k such that (k+1)*prime(k) + k is a prime.

1, 2, 3, 5, 6, 8, 9, 11, 13, 14, 20, 21, 26, 29, 30, 33, 35, 36, 39, 41, 43, 49, 54, 55, 62, 68, 69, 75, 76, 79, 81, 89, 90, 105, 110, 113, 117, 119, 126, 134, 141, 146, 154, 162, 174, 176, 178, 179, 186, 191, 195, 207, 209, 215, 216, 222, 225, 227, 230, 231, 234, 237

Offset: 1

Author

Alex Ratushnyak, Sep 30 2016

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A086172.

Programs

Maple

p:= 1: count:= 0: Res:= NULL:
for n from 1 while count < 100 do
  p:= nextprime(p);
  if isprime(n*p+n+p) then
    count:= count+1; Res:= Res, n
  fi
od:
Res; # Robert Israel, Oct 25 2018

Mathematica

npQ[n_]:=Module[{p=Prime[n]},PrimeQ[n*p+n+p]]; Select[Range[250],npQ] (* Harvey P. Dale, Mar 27 2022 *)

PARI

is(n) = isprime((n + 1) * (prime(n) + 1) - 1); \\ Altug Alkan, Oct 01 2016