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A074875
Numbers n such that sigma(sigma(n)-n) = phi(n).
1
2, 21, 51, 369, 3051, 3783, 5757, 6477, 6897, 7929, 15639, 15925, 20967, 33003, 50739, 58797, 73917, 75627, 118405, 121975, 131979, 170973, 219447, 291369, 310137, 311675, 347337, 365679, 396807, 404559, 437255, 442599, 550719, 558429
OFFSET
1,1
LINKS
EXAMPLE
sigma(sigma(21) - 21) = sigma(32 - 21) = sigma(11) = 12 = phi(21), so 21 is a term of the sequence.
MATHEMATICA
Select[Range[10^5], DivisorSigma[1, DivisorSigma[1, # ] - # ] == EulerPhi[ # ] &]
CROSSREFS
Sequence in context: A330201 A042455 A245546 * A231807 A351118 A097718
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Sep 12 2002
EXTENSIONS
a(19)-a(34) from Donovan Johnson, May 13 2010
STATUS
approved