# You're reading: Posts By Christian Lawson-Perfect

### Exactly how bad is the 13 times table?

Let’s recite the $13$ times table. Pay attention to the first digit of each number:

\begin{array}{l} \color{blue}13, \\ \color{blue}26, \\ \color{blue}39, \\ \color{blue}52 \end{array}

What happened to $\color{blue}4$‽

A while ago I was working through the $13$ times table for some boring reason, and I was in the kind of mood to find it really quite vexing that the first digits don’t go $1,2,3,4$. Furthermore, $400 \div 13 \approx 31$, so it takes a long time before you see a 4 at all, and that seemed really unfair.

### The OEIS now contains 300,000 integer sequences

The Online Encyclopedia of Integer Sequences just keeps on growing: at the end of last month it added its 300,000th entry.

Especially round entry numbers are set aside for particularly nice sequences to mark the passing of major milestones in the encyclopedia’s size; this time, we have four nice sequences starting at A300000. These were sequences that were originally submitted with indexes in the high 200,000s but were bumped up to get the attention associated with passing this milestone.

### Proof by sedition

$n > 2$

An unexpected bit of controversy involving mathematical notation hit the internet last week, when China's government briefly blocked all Chinese internet users from viewing any page or message containing the letter n﻿.

Apparently, those in charge of the Great Firewall feared that those who disapproved of Xi Jinping removing the two-term limit on his presidency of China would use the letter n to refer to the now-arbitrary number of terms for which he can remain in power.

There's some more context in a post by Victor Mair on Language Log, and in the Guardian.

### Faces of Women in Mathematics

This is nice for International Women's Day. Filmmaker Irina Linke and mathematician ﻿Eugénie Hunsicker have put together this montage of women in maths from all around the world.

### Stanisław Ulam biopic

There's going to be a biopic of physicist/mathematician Stanisław Ulam, titled Adventures of a Mathematician﻿.

Hollywood seems to be working its way through 20th century mathematicians – off the top of my head, there have recently been biopics of John Nash, Alan Turing, Stephen Hawking and Srinivasa Ramanujan. What I want to know is, when do we get Michael Sheen playing John Horton Conway?

There's some information about Adventures of a Mathematician, starring Jakub Gierszal as Ulam, at ScreenDaily.