

A069155


Nonprime numbers n such that (n+1)*Sum_{dn} 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
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OFFSET

1,2


COMMENTS

Or, nonprime numbers n such that Sum_{ d dividing n} C(n,d+1)/C(n,d) is an integer.


LINKS

Table of n, a(n) for n=1..35.


MATHEMATICA

Select[Range[2, 1250000], ! PrimeQ[ # ] && IntegerQ[( # + 1)*Apply[Plus, 1/(Divisors[ # ] + 1)]] & ]


CROSSREFS

Sequence in context: A119334 A321780 A074977 * A107352 A127761 A337898
Adjacent sequences: A069152 A069153 A069154 * A069156 A069157 A069158


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



