A156560 Primes of the form 2^n-5.

3, 11, 59, 251, 1019, 4091, 262139, 1048571, 67108859, 4294967291, 68719476731, 72057594037927931, 73786976294838206459, 332306998946228968225951765070086139, 1361129467683753853853498429727072845819, 1427247692705959881058285969449495136382746619

Offset: 1

Author

Vincenzo Librandi, Feb 10 2009

Keywords

• nonn

Comments

If p = 2^n-5 is prime, then p*2^(n-1) is abundant with abundance 4 (see A088832). - Davide Rotondo, Oct 25 2020

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..28

Crossrefs

Corresponding n's are in A059608.

Cf. A088832.

Programs

Magma

[ a: n in [2..500] | IsPrime(a) where a is 2^n-5 ];

Mathematica

Select[Table[2^n-5,{n,2,400}],PrimeQ] (* Vincenzo Librandi, Jul 26 2012 *)

PARI

for(n=1,300,q=2^n-5;if(isprime(q),print(q))) /* gives more terms in <10secs */ \\ Joerg Arndt, Dec 03 2010

Formula

a(n) = 2^A059608(n) - 5.

Extensions

Edited by Zak Seidov