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A072278
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Numbers n such that phi(n) is the sum of the first k divisors of n for some k.
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2
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1, 2, 18, 42, 48, 72, 152, 210, 378, 462, 765, 1242, 1440, 2080, 2528, 2604, 4480, 6336, 8720, 17248, 17664, 21800, 45675, 84456, 106272, 122220, 318400, 344400, 532016, 654848, 1002456, 1707840, 1904640, 4355190, 5688540, 6600128, 7985628
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| The majority are congruent to 0 modulo 6.
29292581888, 38187663360, 97473314304, 114918027264, 147840201728 and 208686261248 are also terms. - Donovan Johnson, Aug 30 2011
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LINKS
| Donovan Johnson, Table of n, a(n) for n = 1..60 (terms < 2*10^10)
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EXAMPLE
| 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.
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MATHEMATICA
| Select[Range[10000], MemberQ[FoldList[Plus, 0, Divisors[#]], EulerPhi[#]] &] (* T. D. Noe, Aug 29 2011 *)
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CROSSREFS
| Sequence in context: A050594 A098857 A189333 * A131538 A009820 A126909
Adjacent sequences: A072275 A072276 A072277 * A072279 A072280 A072281
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jul 09 2002
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EXTENSIONS
| Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 15 2002
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