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 A195106 Numbers with largest and smallest prime factors differing by 4. 3
 21, 63, 77, 105, 147, 189, 221, 315, 437, 441, 525, 539, 567, 735, 847, 945, 1029, 1323, 1517, 1575, 1701, 2021, 2205, 2625, 2835, 2873, 3087, 3675, 3757, 3773, 3969, 4725, 4757, 5103, 5145, 5929, 6557, 6615, 7203, 7875, 8303, 8505, 9261, 9317, 9797, 10051 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..250 Eric Weisstein's World of Mathematics, Cousin Primes EXAMPLE a(10) = 441 = 3^2 * 7^2; a(11) = 525 = 3 * 5^2 * 7; a(12) = 539 = 7^2 * 11. MATHEMATICA pf4Q[n_]:=Module[{pfs=Transpose[FactorInteger[n]][[1]]}, Max[pfs]- Min[pfs]==4]; Select[Range[11000], pf4Q] (* Harvey P. Dale, Sep 24 2011 *) PROG (Haskell) a195106 n = a195106_list !! (n-1) a195106_list = filter (\x -> a006530 x - a020639 x == 4) [1, 3..] CROSSREFS Cf. A195118, A143206; A143203 is a subsequence. Sequence in context: A081302 A058100 A219856 * A143203 A082060 A025525 Adjacent sequences:  A195103 A195104 A195105 * A195107 A195108 A195109 KEYWORD nonn AUTHOR Reinhard Zumkeller, Sep 13 2011 STATUS approved

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Last modified October 13 20:38 EDT 2019. Contains 327981 sequences. (Running on oeis4.)