John D. Cook
johndcook.bsky.social
John D. Cook
@johndcook.bsky.social
Mathematician, data privacy consultant

See also @johndcook.mathstodon.xyz.ap.brid.gy
September 24, 2025 at 3:10 PM
Looking back at Martin Gardner’s RSA article

www.johndcook.com/blog/2025/08...
August 5, 2025 at 1:04 PM
Gluons, quarks, letters, and envelopes

www.johndcook.com/blog/2025/03...
March 17, 2025 at 1:28 AM
New post: Practical consequences of LLM tokenization details

www.johndcook.com/blog/2025/03...
March 9, 2025 at 2:20 PM
February 13, 2025 at 2:49 PM
Polynomial Encounters of the Third Kind

www.johndcook.com/blog/2025/02...
February 13, 2025 at 12:56 PM
Does DeepSeek demonstrate that we don’t need as much compute power as we thought?

www.johndcook.com/blog/2025/02...
February 3, 2025 at 8:04 PM
January 31, 2025 at 5:44 PM
New podcast interview just dropped.

Protecting Privacy in the Age of AI: A Conversation with John Cook

www.trenegy.com/podcast/prot...
Protecting Privacy in the Age of AI: A Conversation with John Cook
We discuss safeguarding sensitive information in data-intensive industries, the balance of preserving data utility and protecting privacy as AI applications raise new concerns, and methods like differ...
www.trenegy.com
January 16, 2025 at 10:07 PM
How the day of the week for New Years Day goes through a 28 year cycle.

The green diamonds represent leap years and the blue squares represent ordinary years.
January 1, 2025 at 3:22 AM
Modal logic and science fiction

www.johndcook.com/blog/2022/01...
December 31, 2024 at 1:08 AM
Unix Time and a Modest Proposal

www.johndcook.com/blog/2024/12...
Unix Time and a Modest Proposal
Why Unix time is not exactly what it is often described to be, and a proposal for fixing it.
www.johndcook.com
December 27, 2024 at 6:13 PM
Centered triangular numbers are the number of dots in images such as the one below.

The nth centered triangular number equals 1 + 3n(n + 1)/2.
December 25, 2024 at 3:47 PM
Most popular posts of 2024

www.johndcook.com/blog/2024/12...
Most popular posts of 2024
Most popular posts on this site in 2024, according to Hacker News.
www.johndcook.com
December 24, 2024 at 3:42 PM
By the nth day of Christmas, my true love had sent to me n(n+1)(n+2)/6 gifts.

www.johndcook.com/blog/2009/12...
Twelve Days of Christmas and tetrahedral numbers
How many gifts are there in the song Twelve Days of Christmas? Day 1: 1 gift Day 2: 1 + 2 = 3 gifts Day 3: 1 + 2 + 3 = 6 gifts … Day 12: 1 + 2 + 3 + … + 12 = 78 gifts The number of gifts on day
www.johndcook.com
December 20, 2024 at 4:59 PM
Intro to interval arithmetic. Applied to cosine iteration.

www.johndcook.com/blog/2024/12...
December 19, 2024 at 4:13 PM
If you press the cosine key on a calculator over and over, you always get stuck on the same number.

This post takes a more sophisticated look at a child’s amusement.

www.johndcook.com/blog/2024/12...
December 17, 2024 at 6:05 PM
A golden hospital gown is an allusion to The Emperor’s New Clothes, except the emperor is somewhere between sumptuously clothed and naked.

www.johndcook.com/blog/2024/12...
December 16, 2024 at 1:10 PM
How many ways can you select six points in the plane so that every subset of three points forms the vertices of an isosceles triangle?

www.johndcook.com/blog/2024/12...
December 9, 2024 at 2:17 PM
Connecting powers of two and decibels

www.johndcook.com/blog/2022/02...
Connecting powers of two and decibels
Powers of two give the approximate significant figures in integer decibels.
www.johndcook.com
December 8, 2024 at 2:08 AM
How to memorize the ASCII table

www.johndcook.com/blog/2022/05...
December 7, 2024 at 7:58 PM
December 5, 2024 at 1:55 PM
December 3, 2024 at 10:58 PM
My Mastodon posts are automatically posted to the Bluesky account @johndcook.mathstodon.xyz.ap.brid.gy
November 30, 2024 at 9:10 PM