Mahaviracharya/Ganita Sara Samgraha/Chapter VI/289

: Chapter $\text {VI}$: Mixed Problems: Problem $289$
Arrows, if they are thin cylinders, circular in cross-section, can be packed in hexagonal bundles.

Let the arrows around the circumference be $18$ in number.

How many in all are the arrows to be found in the bundle in the quiver?

Solution

 * $37$

Proof
The arrows are packed as centered hexagonal numbers.

The answer is immediately apparent.