A382352 Numbers k such that the sum of the reciprocals of the indices of distinct prime factors of k is an integer.
1, 2, 4, 8, 16, 32, 64, 128, 195, 256, 390, 512, 585, 780, 975, 1024, 1170, 1560, 1755, 1950, 2048, 2340, 2535, 2925, 3120, 3510, 3900, 4096, 4680, 4875, 5070, 5265, 5850, 6240, 7020, 7605, 7800, 8192, 8775, 9360, 9750, 10101, 10140, 10530, 11700, 12480, 12675, 14040, 14625
Offset: 1
Keywords
Programs
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Mathematica
Join[{1}, Select[Range[2, 15000], IntegerQ[Plus @@ (1/PrimePi[#[[1]]] & /@ FactorInteger[#])] &]] -
PARI
isok(k) = my(f=factor(k)); denominator(sum(i=1, #f~, 1/primepi(f[i,1]))) == 1; \\ Michel Marcus, Mar 22 2025