OFFSET
1,1
COMMENTS
a(n) = 8 if and only if n is an odd prime.
EXAMPLE
Illustration of a(9) = 14:
4
_ _ _ _ _
|_ _ _ _ _|
|_ _ 6
|_ |
|_|_ _
| |
| |
| | 4
| |
|_|
.
For n = 9 the symmetric representation of sigma(9) has three parts from right to left as follows: a rectangle, a concave hexagon and a rectangle. The number of edges of the polygons are 4, 6, 4 respectively, therefore the total number of edges is 4 + 6 + 4 = 14, so a(9) = 14.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Omar E. Pol, May 04 2023
STATUS
approved