2026-04-19T02:16:26Z https://yabu.me David Radcliffe https://yabu.me/npub1pw2rh2nqkzxydlgwfwd6s4x5vulpt9zezfjwrhe550lccj6lejxs2n6cn4 https://media.mathstodon.xyz/accounts/avatars/000/004/503/original/3f8e99d73e9df926.png https://media.mathstodon.xyz/accounts/avatars/000/004/503/original/3f8e99d73e9df926.png https://yabu.me/nevent1qqsykwjwk8ck9nd78htvmlrm0gpm8jgp3tw6jhst0jdn5yzwdg0enuczyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6dxaefa In reply to <a href='/nevent1qqsvxlelkhe7u0f2qkd5rmta34tvxf6yt9uymj8hdksmf03n2lgy6fqzz4aqc'>nevent1q…4aqc</a><br/>_________________________<br/><br/>Here is my writeup. I am preparing an article on lower bounds of digital sums.<br/> <img src="https://media.mathstodon.xyz/media_attachments/files/115/667/600/913/213/502/original/d42b96d705fe4f3e.png"> <br/> 2025-12-05T15:13:39Z https://yabu.me/nevent1qqsvkkcdv4ym6n65t6q3h0dgxgmvmyazzr76hhgls5dy7c7uhch4y5qzyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6wle6pc Everybody knows that the sum of the decimal digits of a multiple of 9 is also a multiple of 9. But did you know that the digit sum of a positive multiple of 999 is always 27 or more? 2025-12-04T19:04:30Z https://yabu.me/nevent1qqsqtfuxpwypgl7whhe6p0vvfqvjnd4956ncqcpsfza4ycy3u6vtvlszyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg64z9nks I made a puzzle app to explore an unsolved problem in group theory. I tried to make it intelligible to non-mathematicians. What do you think? <a href="https://radcliffe.github.io/01matrixpuzzle/">https://radcliffe.github.io/01matrixpuzzle/</a> 2025-07-15T02:49:21Z https://yabu.me/nevent1qqsytszwtzkwum3zlcu7pn7s6tpnqlttm6kdk3klgdx7jk3c8r49w8szyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6rgtdzv I have a question that&#39;s too silly for Math Overflow. There&#39;s a famous trick for swapping two integers in three steps, without using a temporary variable:<br/><br/>a ← a + b<br/>b ← a − b<br/>a ← a − b<br/><br/>This can be generalized to cyclic permutations, e.g.<br/><br/>a ← a + b + c<br/>b ← a − b − c<br/>c ← a − b − c<br/>a ← a − b − c<br/><br/>How many steps are needed to realize an arbitrary permutation? Assume that each step replaces one variable with a fixed integer combination of all of the variables. 2025-07-07T21:55:36Z https://yabu.me/nevent1qqsrdlxtzst4judwkc7tmn229lqhhwdxr3ypkerj62g9gfsc2raa2pszyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6h3d2s5 In reply to <a href='/nevent1qqspyyt2s0ayfupad0gj3gldhhn5dfdk6y458tdk3jtzza65n3ylzqgjdar29'>nevent1q…ar29</a><br/>_________________________<br/><br/>I thought that she was talking about academic feminism in particular. The aphorism seems absurd if it&#39;s taken to mean all tools used by an oppressor. 2025-01-29T17:44:40Z https://yabu.me/nevent1qqs9y5msyvv9n3rj8xupafqcu6ppvajw6x4yf9mrn9n6gkc4as3rqeczyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6q7rrq3 Find a sequence of 1000 positive integers in arithmetic progression whose digit sums in base 10 are equal. 2024-09-19T20:53:23Z https://yabu.me/nevent1qqsdzjlrladlfk4aajwr8nrm0klwvc9ppzs5kf6kzmgala2jww909hczyq9egwa2vzcgc3hape9eh2z563nnu9v5tyfxfcwlxj3llrzttlxg6awtcl9 Who is a great math video creator that few people know about? I&#39;m a fan of 3blue1brown and Mathologer, but they have enough supporters already. 2024-09-09T13:56:11Z