Triangular number

Rare card · No. 66268

The triangular numbers or triangle numbers are the sequence of positive integers that can be represented as a lattice of points arranged in an equilateral triangle. The triangular lattice representing the n {\displaystyle n} th triangular number contains n {\displaystyle n} rows: the first row contains one point, the second row contains two, and this pattern continues up to the n {\displaystyle n} th row, which contains n {\displaystyle n} . Therefore, the triangular numbers may also be represented by the formula. T n = 1 + 2 + 3 + ⋯ + ( n − 1 ) + n = ∑ k...

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