Mengoli, Pietro (1650). "Praefatio [Preface]". Novae quadraturae arithmeticae, seu De additione fractionum [New arithmetic quadrature (i.e., integration), or On the addition of fractions]. Bologna: Giacomo Monti.Mengoli's proof is by contradiction:
Bernoulli, Johann (1742). "Corollary III of De seriebus varia". Opera Omnia. Lausanne & Basel: Marc-Michel Bousquet & Co. vol. 4, p. 8.Johann Bernoulli's proof is also by contradiction. It uses a telescopic sum to represent each term 1n as
Thomas Schmelzer and Robert Baillie (Jun 2008). "Summing a Curious, Slowly Convergent Series". The American Mathematical Monthly. 115 (6): 545–540. JSTOR27642532.