e (mathematical constant):
"The number e is one of the most important numbers in mathematics, alongside the additive and multiplicative identities 0 and 1, the imaginary unit i, and π."
"...an account that starts at $1, and yields (1+R) dollars at simple interest, will yield e^R dollars with continuous compounding."
"In contemporary internet culture, individuals and organizations frequently pay homage to the number e. For example, in the IPO filing for Google, in 2004, rather than a typical round number amount of money, the company announced its intention to raise $2,718,281,828, which is e billion dollars to the nearest dollar."
"In another instance, the eminent computer scientist Donald Knuth let the version numbers of his program METAFONT approach e. The versions are 2, 2.7, 2.71, 2.718, and so forth."
e^(i*x) = cos(x)+i*sin(x)