Distances in a bee's honeycomb
Problem 354
Consider a honey bee's honeycomb where each cell is a perfect regular hexagon with side length .

One particular cell is occupied by the queen bee.
For a positive real number , let count the cells with distance from the queen bee cell (all distances are measured from centre to centre); you may assume that the honeycomb is large enough to accommodate for any distance we wish to consider.
For example, , and .
For a positive real number , let count the cells with distance from the queen bee cell (all distances are measured from centre to centre); you may assume that the honeycomb is large enough to accommodate for any distance we wish to consider.
For example, , and .
Find the number of such that .