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A076532
Numbers n such that sopf(sigma(n)) = sigma(sopf(n)), where sopf(x) = sum of the distinct prime factors of x.
8
2, 90, 425, 490, 605, 630, 726, 735, 750, 816, 2250, 2695, 3185, 3234, 3420, 3822, 4176, 5096, 5250, 6591, 7644, 8470, 9100, 9425, 10296, 10780, 11616, 11638, 12321, 15750, 16940, 18096, 22736, 23276, 25578, 27360, 27783, 28500, 31900, 36400
OFFSET
1,1
LINKS
EXAMPLE
sopf(sigma(90)) = sopf(234) = 18; sigma(sopf(90)) = sigma(10) = 18, hence 90 is a term of the sequence.
MATHEMATICA
p[n_] := Apply[Plus, Transpose[FactorInteger[n]][[1]]]; Select[Range[2, 10^4], p[DivisorSigma[1, # ]] == DivisorSigma[1, p[ # ]] &]
PROG
(PARI) isok(n) = (n>1) && sigma(sopf(n)) == sopf(sigma(n)); \\ Michel Marcus, Oct 04 2019
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Oct 18 2002
EXTENSIONS
Edited and extended by Ray Chandler, Feb 13 2005
STATUS
approved