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A152442
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n is included if the largest divisor of n that is coprime to d(n) is a composite, where d(n) is the number of divisors of n.
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1
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4, 15, 16, 21, 25, 27, 30, 33, 35, 36, 39, 42, 49, 50, 51, 54, 55, 57, 64, 65, 66, 69, 70, 75, 77, 78, 81, 85, 87, 91, 93, 95, 98, 100, 102, 105, 110, 111, 114, 115, 119, 120, 121, 123, 125, 129, 130, 133, 135, 138, 140, 141, 143, 144, 145, 147, 150, 154, 155, 159, 161
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| A137926(a(n)) is composite for all n.
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MATHEMATICA
| a = {}; For[n = 2, n < 1000, n++, b = Max[Select[Divisors[n], GCD[DivisorSigma[0, n], # ] == 1 &]]; If[b > 1 && ! PrimeQ[b], AppendTo[a, n]]]; a [From Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Dec 06 2008]
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CROSSREFS
| A137926, A152444
Sequence in context: A163773 A076349 A175959 * A161769 A135658 A066862
Adjacent sequences: A152439 A152440 A152441 * A152443 A152444 A152445
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Dec 04 2008
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EXTENSIONS
| More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and Ray Chandler (rayjchandler(AT)sbcglobal.net), Dec 06 2008
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