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A239274
Numbers k such that k' = sigma(k) - phi(k), where k' = A003415(k) is the arithmetic derivative of k.
0
1, 88, 1104, 492624, 30818736, 200827760, 1598249556, 4575586644, 8491046375, 8554970196, 29917317500, 54481242640, 202195886375, 3201891498000
OFFSET
1,2
COMMENTS
a(15) > 10^13.
MATHEMATICA
ad[1]=0; ad[n_]:=n*Total[(#1[[2]] / #1[[1]]&) /@ FactorInteger[n]]; Select[Range[500000], ad[#] == DivisorSigma[1, #] - EulerPhi[#] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Mar 13 2014
STATUS
approved