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A087699 Greater twin prime p such that 2^p-1 is composite. 1
43, 73, 103, 109, 139, 151, 181, 193, 199, 229, 241, 271, 283, 313, 349, 421, 433, 463, 523, 571, 601, 619, 643, 661, 811, 823, 829, 859, 883, 1021, 1033, 1051, 1063, 1093, 1153, 1231, 1291, 1303, 1321, 1429, 1453, 1483, 1489, 1609, 1621, 1669, 1699, 1723 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
Look at all twin primes (p1, p2); if 2^p2 - 1 is composite print p2.
LINKS
MATHEMATICA
Transpose[Select[Partition[Prime[Range[300]], 2, 1], Last[#]-First[#] == 2&&!PrimeQ[2^Last[#]-1]&]][[2]] (* Harvey P. Dale, Oct 20 2013 *)
PROG
(PARI) twopm1(n) = { forprime(x=2, n, y=2^x-1; if(!isprime(y) && isprime(x-2), print1(x", ") ) ) }
CROSSREFS
Sequence in context: A141971 A144974 A144975 * A054807 A285017 A139932
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Oct 25 2003
EXTENSIONS
Corrected and extended by Ray Chandler, Nov 07 2003
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)