|
%I #15 Apr 14 2017 04:37:16
%S 1,2,18,42,48,72,152,210,378,462,765,1242,1440,2080,2528,2604,4480,
%T 6336,8720,17248,17664,21800,45675,84456,106272,122220,318400,344400,
%U 532016,654848,1002456,1707840,1904640,4355190,5688540,6600128,7985628
%N Numbers n such that phi(n) is the sum of the first k divisors of n for some k.
%C The majority are congruent to 0 modulo 6.
%C 29292581888, 38187663360, 97473314304, 114918027264, 147840201728 and 208686261248 are also terms. - Donovan Johnson, Aug 30 2011
%H Giovanni Resta, <a href="/A072278/b072278.txt">Table of n, a(n) for n = 1..66</a> (terms < 10^11, first 60 terms from Donovan Johnson)
%e The divisors of 72 are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72. phi(72) = 24 = 1 + 2 + 3 + 4 + 6 + 8; hence 72 belongs to the sequence.
%t Select[Range[10000], MemberQ[FoldList[Plus, 0, Divisors[#]], EulerPhi[#]] &] (* _T. D. Noe_, Aug 29 2011 *)
%t Select[Range[8*10^6],MemberQ[Accumulate[Divisors[#]],EulerPhi[#]]&] (* _Harvey P. Dale_, Nov 11 2014 *)
%K nonn
%O 1,2
%A _Joseph L. Pe_, Jul 09 2002
%E Edited and extended by _Robert G. Wilson v_, Jul 15 2002
|
