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 A183072 Positive integers k such that 2^k - 1 is composite and each of its prime divisors has the form 4j + 3. 7
 6, 10, 14, 15, 26, 30, 34, 38, 43, 51, 62, 65, 79, 85, 86, 93, 95, 122, 129, 130, 133, 158, 170, 193, 254, 255, 301, 311, 331, 349, 389, 445, 557, 577, 579, 631, 647, 1103, 1167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Needed factorizations are in the Cunningham Project. LINKS S. S. Wagstaff, Jr., The Cunningham Project. FORMULA A183076(n) = 2^a(n) - 1. EXAMPLE 6 is in this sequence because 2^6 - 1 = 3^2 * 7, and 3 and 7 have the form 4j + 3. MATHEMATICA c4j3Q[n_]:=Module[{c=2^n-1}, CompositeQ[c]&&AllTrue[(#-3)/4&/@ FactorInteger[ c] [[All, 1]], IntegerQ]]; Select[Range[650], c4j3Q] (* Requires Mathematica version 10 or later *) (* The program takes a long time to run *) (* Harvey P. Dale, Sep 23 2018 *) CROSSREFS Cf. A000043, A136003, A183071, A183073, A183074. Cf. A000668, A136005, A183075, A183076, A183077, A183078. Sequence in context: A162409 A226494 A242920 * A225704 A228301 A193416 Adjacent sequences: A183069 A183070 A183071 * A183073 A183074 A183075 KEYWORD nonn,hard,more AUTHOR Stuart Clary, Dec 23 2010 EXTENSIONS a(38)-a(39) from Amiram Eldar, Feb 18 2019 STATUS approved

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Last modified January 27 12:24 EST 2023. Contains 359840 sequences. (Running on oeis4.)