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Odd nonprimes such that the arithmetic mean of all prime factors is not an integer.
5

%I #12 Sep 17 2017 21:44:22

%S 1,45,63,75,99,117,135,147,153,165,171,175,207,245,255,261,273,279,

%T 315,325,333,345,351,363,369,375,385,387,399,405,423,435,455,459,475,

%U 477,495,507,531,539,549,561,567,595,603,615,639,651,657,665,675,705,711,715,735

%N Odd nonprimes such that the arithmetic mean of all prime factors is not an integer.

%C The presence of 1 (which has no prime factors) is for compatibility with A175352.

%H G. C. Greubel, <a href="/A175761/b175761.txt">Table of n, a(n) for n = 1..5000</a>

%F Equals: Intersection of A175352 and A014076.

%e a(6) = 117 because 117 = 3*3*13 and (3 + 3 + 13)/3 is not an integer.

%t fQ[n_] := Block[{fi = Flatten[ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@ n]}, len = Length@ fi; len != 1 && ! IntegerQ[ Plus @@ fi/len]]; Join[{1},Select[1 + 2 Range@ 356, fQ]] (* _Robert G. Wilson v_, Aug 31 2010 *)

%Y Cf. A141468, A175352.

%K nonn,easy

%O 1,2

%A _Juri-Stepan Gerasimov_, Aug 29 2010

%E Corrected (315, 345 inserted, 355 removed) by _R. J. Mathar_, Aug 30 2010

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Last modified September 20 06:43 EDT 2024. Contains 376067 sequences. (Running on oeis4.)