Any number can start a factorial

Any positive number can be found at the beginning of a factorial. That is, for every positive integer n, there is an integer m such that the leading digits of m! are the digits of n. There’s a tradition in math to use the current year when you need an arbitrary numbers; you’ll see this […]

Collatz conjecture skepticism

The Collatz conjecture asks whether the following procedure always terminates at 1. Take any positive integer n. If it’s odd, multiply it by 3 and add 1. Otherwise, divide it by 2. For obvious reasons the Collatz conjecture is also known as the 3n + 1 conjecture. It has been computationally verified that the Collatz […]

Progress on the Collatz conjecture

The Collatz conjecture is for computer science what until recently Fermat’s last theorem was for mathematics: a famous unsolved problem that is very simple to state. The Collatz conjecture, also known as the 3n+1 problem, asks whether the following function terminates for all positive integer arguments n. def collatz(n): if n == 1: return 1 […]

Physical constants in Python

You can find a large collection of physical constants in scipy.constants. The most frequently used constants are available directly, and hundreds more are in a dictionary physical_constants. The fine structure constant α is defined as a function of other physical constants: The following code shows that the fine structure constant and the other constants that […]

Passwords and power laws

According to this paper [1], the empirical distribution of real passwords follows a power law [2]. In the authors’ terms, a Zipf-like distribution. The frequency of the rth most common password is proportional to something like 1/r. More precisely, fr = C r–s where s is on the order of 1. The value of s that […]

Technical notes on math and software

Table of contents Math diagrams Numerical computing Probability Differential equations Python Probability approximations Regular expressions C++ Special functions Typesetting: TeX, HTML, Unicode Emacs R Miscellaneous math My notes on cryptography have their own page. Math diagrams Diagram of probability distribution relationships Modes of convergence Topological properties diagram Category Relationships in Mathematical Physics Category theory definition […]

Leading digits and quadmath

My previous post looked at a problem that requires repeatedly finding the first digit of kn where k is a single digit but n may be on the order of millions or billions. The most direct approach would be to first compute kn as a very large integer, then find it’s first digit. That approach […]

Gelfand’s question

Gelfands’s question asks whether there is a positive integer n such that the first digits of jn base 10 are all the same for j = 2, 3, 4, …, 9. (Thanks to @republicofmath for pointing out this problem.) This post will explore Gelfand’s question via probability. The MathWorld article on Gelfand’s question says that […]