|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
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
|
|
|
MATHEMATICA
|
Select[Range[2, 1250000], ! PrimeQ[ # ] && IntegerQ[( # + 1)*Apply[Plus, 1/(Divisors[ # ] + 1)]] & ]
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Entry revised by N. J. A. Sloane Apr 09 2007 following suggestions by Ryan Propper and Emeric Deutsch.
|
|
STATUS
|
approved
|
|
|
|