John Gietzen
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 Dec 9 awarded Precognitive Sep 3 awarded Taxonomist Jul 29 comment Is there a closed-form equation for $n!$? If not, why not? @ShreevatsaR: Well, because the n! is formally defined as $n!=\prod_{k=1}^n k$, which is not closed form. en.wikipedia.org/wiki/Closed-form_expression an expression is said to be a closed-form expression if, and only if, it can be expressed analytically in terms of a bounded number of certain "well-known" functions. Jul 27 awarded Beta Jul 27 accepted Is there a general formula for solving 4th degree equations? Jul 27 asked Is there a general formula for solving 4th degree equations? Jul 26 comment Algorithm for calculating $A^n$ with as few multiplications as possible Isn't this a Project Euler problem? Jul 25 revised What is the meaning of the double turnstile symbol ($\models$)? edited tags Jul 25 revised How do proof verifiers work? edited tags Jul 25 revised How can there be explicit polynomial equations for which the existence of integer solutions is unprovable? edited tags Jul 25 revised How do the Properties of Relations work? edited tags Jul 23 accepted What is the most efficient way to determine if a matrix is invertible? Jul 23 comment What is the most efficient way to determine if a matrix is invertible? Well, I haven't learned the proof yet... I don't think he even mentioned how it is done... Jul 23 revised Is there a closed-form equation for $n!$? If not, why not? edited tags Jul 23 awarded Organizer Jul 23 revised Unital homomorphism edited tags Jul 23 revised What are all the homomorphisms between the rings $\mathbb{Z}_{18}$ and $\mathbb{Z}_{15}$? edited tags Jul 23 comment What is the most efficient way to determine if a matrix is invertible? Thanks. I imagine that proving that is quite an enormous amount of work. Jul 23 revised What is the most efficient way to determine if a matrix is invertible? added 4 characters in body Jul 23 comment How do you prove that a prime is the sum of two squares iff it is congruent to 1 mod 4? @Akhil: It is acceptable to answer your own question.