Leonhard Euler

Now I will have less distraction.

For a short time, I was able to see with my left eye, but now I have lost that as well. I am like a mole, burrowing in the dark.

My pencil now surpasses me in wisdom.

The number e is of the greatest importance in mathematics.

The sum of all the reciprocals of the triangular numbers is 2.

I have recently found, quite by chance, an extraordinary beautiful and most general theorem...

The series diverges because the sum of the reciprocals of the prime numbers diverges, albeit very slowly.

Thus, between zero and one, there are infinitely many rational numbers, and yet there are infinitely more irrational numbers.

A function of a variable quantity is an analytic expression composed in any way whatsoever of the variable quantity and numbers or constant quantities.

The power of mathematics rests on its evasion of all unnecessary thought and on its wonderful saving of mental operations.

Geometry is the science which restores the problems of analysis to visual perception.

The introduction of the digit 0 or the group concept was general nonsense too, and mathematics was more or less stagnating for thousands of years because nobody was around to take such childish steps...

I have found a very great number of exceedingly beautiful theorems.

The most learned and acute Johann Bernoulli has shown me a new method for integrating differential equations by means of a factor.

It will seem not a little paradoxical to ascribe a great importance to observations even in that part of the mathematical sciences which is usually called Pure Mathematics, since the current opinion is that observations are restricted to physical objects that make an impression on the senses.

The differential calculus is the true metaphysics.

In the meantime, most noble friend, you have assigned the famous 'Basel Problem' to me, which indeed is more difficult than I first thought.

I have now finished a large part of my work on the motion of the moon, but the calculations are so vast that I have had to commit them to a special shorthand of my own invention.

The controversy between Leibniz and Newton concerning the invention of the calculus was a great misfortune for the whole of mathematical science.

The symbol π is now a standard notation for the ratio of the circumference to the diameter of a circle.