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 A242920 Numbers N with prime factors p_1, ... p_n, such that 1/p_1 + sum{i=2..n} p_(i-1)/p_i + p_n/N - (n+2)/N = 1. 1

%I

%S 6,10,14,15,22,26,34,35,38,46,58,62,74,82,86,94,106,118,122,134,142,

%T 143,146,158,166,178,194,202,206,214,218,226,254,262,274,278,298,302,

%U 314,323,326,334,346,358,362,382,386,394,398,422,446,454,458,466,478

%N Numbers N with prime factors p_1, ... p_n, such that 1/p_1 + sum{i=2..n} p_(i-1)/p_i + p_n/N - (n+2)/N = 1.

%H Steve Humble, <a href="http://plus.maths.org/content/surprising-maths-make-your-own-conjecture">Create your own mathematical mysteries</a>, +plus magazine, University of Cambridge.

%e 6=2*3 and 1/2 + 2/3 + 3/6 - 4/6 = 1, so 6 belongs to the sequence.

%o (PARI) isok(n) = f = factor(n)[,1]; 1/f[1] + sum(i=2, #f, f[i-1]/f[i]) + f[#f]/n - (#f~ + 2)/n == 1;

%K nonn

%O 1,1

%A _Michel Marcus_, May 26 2014

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Last modified September 25 16:13 EDT 2020. Contains 337344 sequences. (Running on oeis4.)