I have referred to them twice (here and here) so far. Also, the Euler-Maclaurin formula I discussed in second post, explains a lot about their occurrences (for example). Now I think it’s time to dive deeper and try to understand them.

In 1631, Johann Faulhaber published *Academia Algebra* (it was a German text despite the Latin title). This text contains a generalisation of sums of powers, which in modern notations reads:

Observe that the expression on the right hand side in square brackets appears like binomial expansion, but there are some constant terms multiplied to them (which can also be 0). These constant terms were named “Bernoulli Numbers” by Abraham de Moivre, since they were intensively discussed by Jacob (Jacques) Bernoulli in *Ars Conjectandi* published in Basel in 1713, eight years after his death.

I will follow the notation from The book of numbers (published in 1996). So we will denote Bernoulli number by where

This notation enables us to calculate sum of power of first natural numbers quickly. We can re-write above summation formula as:

To illustrate, how to use this formula, let’s calculate sum of powers of first 1000 natural numbers:

So, we have done binomial expansion of the right hand side and used the fact that . Now we will replace corresponding values of Bernoulli Numbers to get:

*(This answer was cross-checked using SageMath)*

There are many ways to calculate the value of Binomial numbers, but the simplest one is to using the recursive definition:

for k>1, gives value of

There is another definition of Bernoulli Numbers using power series:

This gives slightly different sequence of Bernoulli numbers, since in this , and the recursive definition is

for k>1, gives value of

This definition can be used to calculate val value of , since its infinite series expression has Bernoulli numbers in coefficients.

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I wasn’t aware of this link between Bernoulli numbers and tangent. That’s rather neat.

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Another remarkable relation of Bernoulli numbers is with Riemann Zeta Function!

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Do you think you might write about that at some point?

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I shall write about it in last week of July 2016.

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Oh, good. I’m looking forward to it.

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Sorry, I won’t be able to write about it (as promised) since stuck with some other work.

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