Hexagonal number
A hexagonal number is a figurate number that represents a hexagon. The hexagonal number for n is given by the formula n(2n - 1). The first few hexagonal numbers are
1, 6, 15, 28, 45, 66, 91, 120, 153, 190, 231, 276, 325, 378, 435, 496, 561, 630, 703, 780, 861, 946
Every hexagonal number is a triangular number, but not every triangular number is a hexagonal number. Like a triangular number, the digital root in base 10 of a hexagonal number can only be 1, 3, 6 or 9.
Hexagonal numbers should not be confused with centered hexagonal numbers, which model the standard packaging of Vienna sausages. To avoid ambiguity, hexagonal numbers are sometimes called "cornered hexagonal numbers".
