Check whether the input matrix is a figurate number triangle: http://mathworld.wolfram.com/FigurateNumberTriangle.html
you should probably add a test case where the correct answer is false.
True!
I added a few more tests as suggested.
Which values occur exactly three times?
3308 Solvers
226 Solvers
Find the largest value in the 3D matrix
899 Solvers
378 Solvers
106 Solvers