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A091321
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OU-Sigma perfect numbers.
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4
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6, 28, 90, 120, 496, 8128, 10080, 63700, 220500, 523776, 1323000, 1528800, 2056320
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The OU-Sigma function is defined as OU-Sigma(n) = A107749(n).
Then an OU-Sigma perfect number satisfies OU-Sigma(n) = k*n for some k.
Every perfect number is here because OE-Sigma(2^(m-1)*M_m) = Sigma(2^(m-1))*UnitarySigma(M_m) = Sigma(2^(m-1))*Sigma(M_m) = 2^m*M_m.
Also in the sequence are 33550336, 8589869056, 22144573440, 51001180160, 153003540480, 243643438080, 583125903360, 71724486113280, 1555825650042470400, but there may be missing terms in between.
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EXAMPLE
| Sequence begins 2*3, 2*3^2*5, 2^2*7, 2^2*5^2*7^2*13, 2^3*3*5, 2^4*31, 2^5*3^2*5*7, ...
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CROSSREFS
| Cf. A091322
Sequence in context: A202956 A055711 A141255 * A125310 A138874 A172141
Adjacent sequences: A091318 A091319 A091320 * A091322 A091323 A091324
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KEYWORD
| nonn
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AUTHOR
| Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp), Feb 17 2004
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EXTENSIONS
| Terms 220500 to 2056320 by R. J. Mathar, Jun 02 2011
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