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This 10×10 reentrant knight's tour has the amazing property that a queen at position 99 attacks all of the prime numbers (shown in green). Furthermore, all of the odd numbers attacked by that queen are prime—except the ‘1’, which some people think is prime. Furthermore, the year of my birth just happens to be present, along with 2023.
I'm gettin' kinda old: now nearly one-third of a byte (256÷3). My age is a beautiful binary palindrome, also the product of two Fermat primes!
Germán González-Morris sent me a delicious Pi Day treat, which you can find in the amendment to page 411 on page 5 of the Errata for Volume 4B of The Art of Computer Programming.
The January issue of an excellent mathematics magazine, Bhāvanā, begins with an interview in which two of its editors asked me 40 wide-ranging questions. I decided to answer each of them by using exactly 280 ASCII characters; so, if want to check this, you can look here. (These are the answers without the questions.)
The fourth volume of The Art of Computer Programming deals with Combinatorial Algorithms, the area of computer science where good techniques have the most dramatic effects. I love it the most, because one good idea can often make a program run a million times faster. It's a huge, fascinating subject, and I published Part 1 (Volume 4A, 883 pages, now in its twenty-second printing) in 2011.
Ta da: My publishers told me at the end of September 2022 that Part 2 (732 pages) had just arrived at their warehouse. Shipments began in October and the book was already in its second printing as of November 2022.
Full details, including a dozen reviews from people who have looked closely at previews of the content, appear on the publisher's website.
Preliminary versions of most of this material were published in 2015 and 2019 as Volume 4, Fascicle 6 and Volume 4, Fascicle 5. Errata to those paperbacks, as well as to all the hardcover volumes, can be found on the TAOCP home page.
I've spent considerable time, while preparing many of the new exercises, attempting to improve on expositions that I found in the literature. And in several noteworthy cases, nobody has yet pointed out any errors. It would be nice to believe that I actually got the details right on my first attempt. But that seems unlikely, because I had hundreds of chances to make mistakes. So I fear that the most probable hypothesis is that nobody has been sufficiently motivated to check the finer points out carefully as yet.
I still cling to a belief that such details are extremely instructive. Thus I would like to enter here a plea for some readers to tell me explicitly, “Dear Don, I have read exercise N and its answer very carefully, and I believe that it is 100% correct,” where N is one of the following exercises:
Please don't be alarmed by the highly technical nature of these examples; more than 500 of the other exercises are completely non-scary, indeed quite elementary. But of course I do want to go into high-level details also, for the benefit of advanced readers; and those darker corners of my books are naturally the most difficult to get right. Hence this plea for help.
Remember that you don't have to work the exercise first. You're allowed to peek at the answer; in fact, you're even encouraged to do so. Please send success reports to the usual address for bug reports (email@example.com). Thanks in advance!
By the way, if you want to receive a reward check for discovering an error in TAOCP, your best strategy may well be to scrutinize the answers to the exercises that are listed above.
Meanwhile I continue to work on Part 3 (Volume 4C), which already has many exciting topics of its own. Those sections are still in very preliminary form, but courageous readers who have nothing better to do might dare to take a peek at the comparatively raw copy in these “prefascicles.” One can look, for instance, at Pre-Fascicle 8a (Hamiltonian Paths and Cycles); Pre-Fascicle 9b (A Potpourri of Puzzles). Thanks to Tom Rokicki, those PostScript files are now searchable!
I seem to get older every day, and people keep asking me to reminisce about the glorious days of yore. If you're interested in checking out some of those videos and other archives, take a look at my news page for 2020, which I've updated with a few items captured after that year.
Although I must stay home most of the time and work on yet more books that I've promised to complete, I do occasionally get into speaking mode.