John Gietzen
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 Jul29 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. Jul27 awarded Beta Jul27 accepted Is there a general formula for solving 4th degree equations? Jul27 asked Is there a general formula for solving 4th degree equations? Jul26 comment Algorithm for calculating $A^n$ with as few multiplications as possible Isn't this a Project Euler problem? Jul25 revised What is the meaning of the double turnstile symbol ($\models$)? edited tags Jul25 revised How do proof verifiers work? edited tags Jul25 revised How can there be explicit polynomial equations for which the existence of integer solutions is unprovable? edited tags Jul25 revised How do the Properties of Relations work? edited tags Jul23 accepted What is the most efficient way to determine if a matrix is invertible? Jul23 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... Jul23 revised Is there a closed-form equation for $n!$? If not, why not? edited tags Jul23 awarded Organizer Jul23 revised Unital homomorphism edited tags Jul23 revised What are all the homomorphisms between the rings $\mathbb{Z}_{18}$ and $\mathbb{Z}_{15}$? edited tags Jul23 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. Jul23 revised What is the most efficient way to determine if a matrix is invertible? added 4 characters in body Jul23 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. Jul23 asked What is the most efficient way to determine if a matrix is invertible? Jul22 revised How can you prove that the square root of two is irrational? added 18 characters in body; edited tags; added 2 characters in body