#1028 · Algebra · Sequences & series

Triangular numbers generating function

Find the sum to infinity of $1 + 3 x + 6 x^{2} + 10 x^{3} + \dots$ , assuming $∣ x ∣ < 1$ .

~3 minAnswer checked instantlySequencesSeries

H. S. Hall & S. R. Knight, Higher Algebra (1891) · Ch. V. Geometrical Progression, Examples V.b, No. 6

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Checked against the answer in H. S. Hall & S. R. Knight, Higher Algebra (1891).