495248
[Commentary:
From right to left, the columns list:
units (1, 1, 1, 1,...)
lengths (1, 2, 3, 4,...)
triangular numbers (1, 3, 6, 10,...)
triangular-pyramidal numbers (1, 4, 10, 20,...)
triangular-pyramido-pyramidal numbers (1, 5, 15, ]
units (1, 1, 1, 1,...)
lengths (1, 2, 3, 4,...)
triangular numbers (1, 3, 6, 10,...)
triangular-pyramidal numbers (1, 4, 10, 20,...)
triangular-pyramido-pyramidal numbers (1, 5, 15, ]