A110581 Primes p such that 2p-1 is prime, but 4p-3 is not prime.

3, 7, 31, 37, 97, 139, 157, 199, 211, 229, 271, 307, 337, 367, 379, 547, 577, 601, 607, 661, 691, 727, 811, 877, 937, 967, 997, 1009, 1171, 1237, 1297, 1399, 1429, 1459, 1609, 1627, 1657, 1759, 1867, 2011, 2029, 2137, 2221, 2281, 2467, 2539, 2551, 2557

Offset

1,1

Comments

A subsequence of A005382, primes p such that 2p-1 is also prime. Note that for all n, 2a(n)-1 is not in this sequence.

Links

T. D. Noe, Table of n, a(n) for n=1..1000

Jeffery J. Holt, The minimal number of solutions to phi(n)=phi(n+k), Math. Comp., 72 (2003), 2059-2061.

Mathematica

Select[Prime[Range[2, 1000]], PrimeQ[2#-1] && !PrimeQ[4#-3]&]

Prog

(Magma) [p: p in PrimesUpTo(2600) | IsPrime(2*p-1) and not IsPrime(4*p-3)]; // Vincenzo Librandi, Apr 14 2013

Crossrefs

Sequence in context: A023266 A359702 A217198 * A128436 A213899 A034915

Adjacent sequences: A110578 A110579 A110580 * A110582 A110583 A110584

Keyword

nonn,easy

Author

T. D. Noe, Jul 28 2005

Status

approved