blocks by robinhouston

Parabolic flow

Regex to test for divisibility by 11, in base 9


Plouffe’s prime-generating constant

3×3 troll-square matrices with two-digit entries

Three-digit troll-square matrices

Two-digit troll-square matrices


Search for English words that have a hex representation as a prime number


Assembler source code from







Sage code to find left-truncatable primes in bijective numeration

The left-truncatable primes in base 10 bijective numeration





findBasis([a,b,c,d], 4, [a,b,e]) does not enclose e

Circles animated with WebGL

Matt Day’s in-place permutation algorithm using JavaScript generators

Clamp at each tick

Using transition.attr as usual

D3 circle transitions: longhand

Convert spreadsheet column letters (A,B, …, Z, AA, AB, …) to index numbers, and vice versa

(timer) Force layout issue with D3 v4.0.0 alpha.45

Force layout issue with D3 v4.0.0 alpha.45

D3 Custom Bundle

An axis with a date scale

A different Hilbert curve animation

A worm on a Hilbert curve

Hilbert curves

A Perl program using only the characters &+-.:<=>acemnorsuvwxz~ – see

Testing Safari’s strange treatment of declared global variables


More Moiré

Moiré patterns

All the ways to make $39.75 from coins of denominations 1¢, 5¢, 10¢, 25¢, and $1

Constant flux


A superpermutation on six symbols of length 872

Test case for Safari fullscreen bug

Interactive maze generator

FitzHugh-Nagomo maze generator

A reaction-diffusion simulation using WebGL

Worms 2

Ammonis worms up close and personal

Ammonis worms

Close-up of the chequered grid

Black and white and red all over

How to make a map of the world with D3

Another method for generating “all RGB” images

A 4096×4096 image containing each RGB value once (h/t Z-order traversal of RGB cube mapped to z-order traversal of 4096×4096 square.


A brief explanation of the puzzling tweet


Solve a variant of the “Question 2” homework exercise from a previous iteration of the Coursera _Cryptography I_ course, proposed by Brian Meyer:

Compute the Bang Bang numbers

A family of equal-area projections

Flow experiment II

Experiments in flow

Double stumbling blocks

Stumbling blocks

Spiral triangles

Double Doyle spiral via Möbius transformation

Doyle spiral explorer

Doyle spiral circle packing

Algorithmic painting

Maze flood fill

Dudeney’s hinged triangle-square

Multiple sliders – Talkie demo

Slider – Talkie demo

Countdown – Talkie demo

Head & Shoulders

Simple color animation



Test case for throwing an exception in Java and catching it in C++

what happens when I run a script (bug in survey branch of whatdotheyknow-theme)

lvalue subroutine behaviour changes

A patch for pdftk 1.44 that fixes an infinite-loop bug

A Sleep sort implementation for

Mergesort implementation for

Signatures over time of

The number of perfect mazes on a 100×100 grid

A version of the algorithm that permits arbitrary clustering of crossings



When is an odd prime the sum of two squares?

Number of steps taken when switching from Aldous-Broder to Wilson's algorithm at different points

Make the maze demo from display correctly in IE