Search: id:A020493
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%I A020493
%S A020493 1,3,15,30,35,56,70,78,105,140,168,190,210,248,264,357,420,570,616,630,
%T A020493 714,744,812,840,910,1045,1240,1485,1672,1848,2090,2214,2436,2580,2730,
%U A020493 3080,3135,3339,3596,3720,3956,4064,4180,4522,4674,5016,5049,5278,5396
%N A020493 Numbers n such that d(n) (number of divisors) divides phi(n) (Euler function) 
               divides sigma(n) (sum of divisors).
%C A020493 Numbers n such that sigma_0(n) divides phi(n) divides sigma_1(n).
%D A020493 D. Wells, Curious and interesting numbers, Penguin Books, p. 130
%e A020493 210 has 16 divisors, which divides phi(210)=48, which in turn divides 
               sigma(210)=576, so 210 is a member of the sequence.
%Y A020493 Cf. A000005, A000010, A000203.
%Y A020493 Sequence in context: A147344 A053519 A039666 this_sequence A087183 A106354 
               A018972
%Y A020493 Adjacent sequences: A020490 A020491 A020492 this_sequence A020494 A020495 
               A020496
%K A020493 nonn
%O A020493 1,2
%A A020493 David W. Wilson (davidwwilson(AT)comcast.net)
%E A020493 Wells incorrectly has 52 instead of 56.

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