11

This number is a prime.

The smallest number of a finite set of numbers inscribed on the faces of a Mughal gold box in the shape of an icosahedron: 11, 20, 21, 31, 41, 51, 61, 71, 81, 91, 101, 201, 202, 301, 401, 501, 601, 701, 801, and 901. An accompanying manuscript note records that the box was found in Tipu Sultan's treasury, after the fall of Seringapatam (India) in 1799. Some research has been devoted to the interpretation of the 20 Arabic numerals of this box, which at first appeared to be unrelated. Among the 11 composite numbers of this list, what's the smallest? [Capelle]