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 A161676 Isolated primes p such that 2^p-1 is also a prime number. 0
 2, 89, 127, 607, 2203, 2281, 3217, 4253, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..25. FORMULA A000043 INTERSECT A007510. EXAMPLE For the isolated prime p=2= A007510(1), p^2-1=3 is prime, which adds p=2 to the sequence. MAPLE MP := [2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917]: n := 0: for j to 39 do if `and`(isprime(MP[j]-2) = false, isprime(MP[j]+2) = false) then n := n+1; a[n] := MP[j] else end if end do: seq(a[n], n = 1 .. 25); # Emeric Deutsch, Jun 20 2009 CROSSREFS Cf. A000043, A007510. Sequence in context: A355272 A105268 A139881 * A235467 A249305 A023302 Adjacent sequences: A161673 A161674 A161675 * A161677 A161678 A161679 KEYWORD nonn AUTHOR Vladislav-Stepan Malakhovsky & Juri-Stepan Gerasimov, Jun 16 2009 EXTENSIONS More terms from Emeric Deutsch, Jun 20 2009 Definition rephrased by R. J. Mathar, Sep 23 2009 STATUS approved

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Last modified June 20 12:17 EDT 2024. Contains 373527 sequences. (Running on oeis4.)