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 A127643 Composite numbers n such that n divides A123591(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2. 2
 15, 51, 65, 85, 185, 221, 255, 341, 451, 533, 561, 595, 645, 679, 771, 1059, 1095, 1105, 1271, 1285, 1313, 1387, 1455, 1581, 1729, 1905, 2045, 2047, 2091, 2307, 2465, 2701, 2755, 2821, 2895, 3201, 3205, 3277, 3281, 3341, 3603, 3655, 3723, 3855, 4033, 4039 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS p divides A123591(p) for prime p>2. Odd composite numbers n such that (2^n-1)^(2^n) == 1 (mod n). - Robert Israel, Jul 06 2017 LINKS Robert Israel, Table of n, a(n) for n = 1..571 MAPLE select(n -> not isprime(n) and (2^n-1) &^ (2^n) mod n = 1, [seq(i, i=9..10000, 2)]); # Robert Israel, Jul 06 2017 MATHEMATICA Do[f=PowerMod[(2^n-1), (2^n), n]-1; If[ !PrimeQ[n]&&IntegerQ[(n+1)/2]&&IntegerQ[f/n], Print[n]], {n, 2, 10000}] CROSSREFS Cf. A123591, A085606. Sequence in context: A194851 A075928 A020214 * A227129 A238574 A238575 Adjacent sequences:  A127640 A127641 A127642 * A127644 A127645 A127646 KEYWORD nonn AUTHOR Alexander Adamchuk, Jan 22 2007 STATUS approved

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Last modified September 16 06:48 EDT 2019. Contains 327090 sequences. (Running on oeis4.)