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 A076763 1-apexes of omega: numbers n such that omega(n-1) < omega(n) > omega(n+1), where omega(m) = the number of distinct prime factors of m. 5
 6, 10, 12, 18, 24, 26, 28, 30, 42, 48, 60, 66, 70, 72, 78, 80, 82, 84, 90, 102, 105, 108, 110, 114, 120, 126, 130, 132, 138, 140, 150, 154, 156, 165, 168, 170, 174, 180, 182, 186, 190, 192, 195, 198, 204, 210, 220, 222, 228, 234, 238, 240, 242, 246, 252, 255 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS I call n a "k-apex" (or "apex of height k") of the arithmetical function f if n satisfies f(n-k) < ... < f(n-1) < f(n) > f(n+1) > .... > f(n+k). LINKS G. C. Greubel, Table of n, a(n) for n = 1..5000 EXAMPLE 28 is in the sequence because it has two unique prime factors (2 and 7), more than either of its neighbors 27 (one such factor, namely 3) and 29 (one such factor, 29). - Neil Fernandez, Dec 21 2004 MATHEMATICA omega[n_] := Length[FactorInteger[n]]; Select[Range[3, 500], omega[ # - 1] < omega[ # ] > omega[ # + 1] &] For[i=1, i<1000, If[And[Length[FactorInteger[i-1]]#[[3, 2]]&] (* Harvey P. Dale, Dec 11 2011 *) PROG (PARI) isok(n) = (omega(n-1) < omega(n)) && (omega(n) > omega(n+1)); \\ Michel Marcus, May 06 2017 CROSSREFS Cf. A101932, A001221. Sequence in context: A315130 A315131 A046288 * A064712 A348629 A284667 Adjacent sequences:  A076760 A076761 A076762 * A076764 A076765 A076766 KEYWORD nonn AUTHOR Joseph L. Pe, Nov 13 2002 EXTENSIONS Edited by N. J. A. Sloane, Sep 06 2008 at the suggestion of R. J. Mathar STATUS approved

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Last modified May 28 15:04 EDT 2022. Contains 354115 sequences. (Running on oeis4.)