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A069155
Nonprime numbers n such that (n+1)*Sum_{d|n} 1/(d+1) is an integer.
1
1, 10, 55, 161, 209, 551, 649, 1079, 1189, 3401, 6049, 6319, 9701, 12151, 14279, 14849, 25271, 34399, 40753, 51841, 64769, 85919, 150281, 158801, 193159, 194399, 246401, 286579, 456191, 514999, 546209, 563471, 647351, 920639, 1156609
OFFSET
1,2
COMMENTS
Or, nonprime numbers n such that Sum_{ d dividing n} C(n,d+1)/C(n,d) is an integer.
MATHEMATICA
Select[Range[2, 1250000], ! PrimeQ[ # ] && IntegerQ[( # + 1)*Apply[Plus, 1/(Divisors[ # ] + 1)]] & ]
CROSSREFS
Sequence in context: A119334 A321780 A074977 * A107352 A127761 A337898
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 08 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, Apr 30 2002
Entry revised by N. J. A. Sloane Apr 09 2007 following suggestions by Ryan Propper and Emeric Deutsch.
STATUS
approved