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Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this result was known 300 years before to the Kerala School (India) identified with Madhava (see e.g. Borwein 2014; pdf).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds doubles the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).

Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this identity was known 300 years before to the Kerala School (India) identified with Madhava (see e.g. Borwein 2014; pdf).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds doubles the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).

Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this result was known 300 years before to the Kerala School (India) identified with Madhava (see e.g. Borwein 2014; pdf).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds duplicates the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).

Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this result was known 300 years before to the Kerala School (India) identified with Madhava (see e.g. Borwein 2014; pdf).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds doubles the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).

Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this result was known 300 years before to the Kerala School (India) identified with Madhava (see this paper).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds duplicates the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).

Leibniz proved that $$1-\frac13+\frac15-\frac17+\frac19-\frac{1}{11}+\cdots = \frac{\pi}{4},$$ in 1674. However this result was known 300 years before to the Kerala School (India) identified with Madhava (see e.g. Borwein 2014; pdf).

In 1976 E. Salamin and R. Brent obtained independently a formula for approximating the number $\pi$ which is quadratically convergent; that is, every term one adds duplicates the number of correct digits of $\pi$. We now know that this formula had been already proved by Gauss. It appears on page 6 of handbook 6, "Short Essays from various fields of mathematics, begun in May 1809", but the formula was forgotten. One reason could be that it is not of practical use if one has to make the calculations by hand. For more information see the chapter 7 of the book "$\pi$ unleashed" by J. Arndt and C. Haenel (Springer).