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A110581 Primes p such that 2p-1 is prime, but 4p-3 is not prime. 3
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 (list; graph; refs; listen; history; text; internal format)
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: A080173 A023266 A217198 * A128436 A213899 A034915

Adjacent sequences:  A110578 A110579 A110580 * A110582 A110583 A110584

KEYWORD

nonn,easy

AUTHOR

T. D. Noe, Jul 28 2005

STATUS

approved

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Last modified February 21 18:05 EST 2020. Contains 332107 sequences. (Running on oeis4.)