|
Search: id:A069155
|
|
|
| A069155 |
|
Nonprime numbers n such that (n+1)*Sum_{d|n} 1/(d+1) is an integer. |
|
+0
2
|
|
| 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; listen)
|
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
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: A088404 A119334 A074977 this_sequence A107352 A127761 A070212
Adjacent sequences: A069152 A069153 A069154 this_sequence A069156 A069157 A069158
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 08 2002
|
|
EXTENSIONS
|
Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 30 2002
Entry revised by njas Apr 09 2007 following suggestions by Ryan Propper and Emeric Deutsch.
|
|
|
Search completed in 0.002 seconds
|
