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Search: id:A072278
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| A072278 |
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Phi(n) is the sum of the first k divisors of n for some k. |
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+0
1
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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
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OFFSET
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1,2
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COMMENT
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The majority are congruent to 0 modulo 6.
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EXAMPLE
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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
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a = {}; For[j = 1, j <= 10^7, j++, s = 0; d = Divisors[j]; l = Length[d]; e = EulerPhi[j]; For[i = 1, i <= l, i++, s = s + d[[i]]; If[s == e, a = Append[a, j]; Break]]]; a
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CROSSREFS
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Sequence in context: A137308 A050594 A098857 this_sequence A131538 A009820 A126909
Adjacent sequences: A072275 A072276 A072277 this_sequence A072279 A072280 A072281
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jul 09 2002
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EXTENSIONS
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Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 15 2002
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