OFFSET
1,1
COMMENTS
EXAMPLE
The symmetric representation of sigma(9) = 13 in the first quadrant looks like this:
y
.
._ _ _ _ _ 5
|_ _ _ _ _|
. |_ _ 3
. |_ |
. |_|_ _ 5
. | |
. | |
. | |
. | |
. . . . . . . . |_| . . x
.
There are three parts: 5 + 3 + 5 = 13, so 9 is in the sequence because the structure contains at least two parts of distinct size.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Omar E. Pol, Dec 19 2015
STATUS
approved