A139481 -id:A139481 - cp's OEIS frontend

A139480 a(n) = A000043(n) - 3.

0, 2, 4, 10, 14, 16, 28, 58, 86, 104, 124, 518, 604, 1276, 2200, 2278, 3214, 4250, 4420, 9686, 9938, 11210, 19934, 21698, 23206, 44494, 86240, 110500, 132046, 216088, 756836, 859430, 1257784, 1398266, 2976218, 3021374, 6972590, 13466914, 20996008, 24036580, 25964948

Offset: 2

Artur Jasinski, Apr 22 2008

nonn

2^a(n)-1 is divisible by 3. For (2^a(n)-1)/3 see A124477.

For a(n)/2 see A139481.

Amiram Eldar, Table of n, a(n) for n = 2..48

Cf. A000043, A000668, A124477, A139479, A139481.

MersennePrimeExponent[Range[2, 48]] - 3 (* Amiram Eldar, Oct 17 2024 *)

Definition corrected by Omar E. Pol, May 23 2008
Edited by N. J. A. Sloane, May 23 2008
a(40)-a(42) from Amiram Eldar, Oct 17 2024

A174288 Primes p such that 8*2^(2p)-1 is also prime.

Original entry on oeis.org

2, 5, 7, 29, 43, 1607, 4969, 9967, 22247, 699133, 1510687, 21321899

Offset: 1

Vincenzo Librandi, Mar 15 2010

These are the primes in A139481. - R. J. Mathar, Mar 17 2010

			For p = 2, 8*2^4-1 = 127; p = 5, 8*2^10-1 = 8191; p = 7, 8*2^14-1 = 131071.

Cf. A139481.

[p: p in PrimesUpTo(4500)| IsPrime(8*2^(2*p)-1)];

Select[(MersennePrimeExponent[Range[48]] - 3) / 2, PrimeQ] (* Amiram Eldar, Jul 14 2025 *)

a(7)-a(10) from Vincenzo Librandi, Jul 13 2025

a(11)-a(12) from Amiram Eldar, Jul 14 2025

cp's OEIS Frontend

A139480 a(n) = A000043(n) - 3.

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