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A075027
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Define a number k to occupy a divisor pole if d(k-1) < d(k) > d(k+1) where d(k) is the number of divisors of k. Sequence gives numbers occupying a divisor pole.
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3
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4, 6, 8, 10, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 48, 50, 52, 54, 56, 60, 64, 66, 68, 70, 72, 78, 80, 84, 88, 90, 92, 96, 100, 102, 108, 110, 112, 114, 120, 124, 126, 128, 130, 132, 138, 140, 144, 150, 152, 154, 156, 160, 162, 165, 168, 170, 174, 176, 180
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Obviously every term is composite. The average of a twin prime pair is a member.
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LINKS
| Harvey P. Dale, Table of n, a(n) for n = 0..1000
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EXAMPLE
| 10 is here since d(9) = 3, d(10) = 4, d(11) = 2 and 3 < 4 > 2.
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MATHEMATICA
| #[[2, 1]]&/@Select[Partition[Table[{n, DivisorSigma[0, n]}, {n, 200}], 3, 1], #[[1, -1]]<#[[2, -1]]>#[[3, -1]]&] (* From Harvey P. Dale, Oct 09 2011 *)
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CROSSREFS
| Cf. A075025, A075026.
Sequence in context: A053226 A074827 A068354 * A076298 A194579 A194594
Adjacent sequences: A075024 A075025 A075026 * A075028 A075029 A075030
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 02 2002
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EXTENSIONS
| More terms from Jason Earls (zevi_35711(AT)yahoo.com), Sep 04 2002
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