This is a copy of Ben Despres' original web page about Lychrel numbers that was located at: ""

I have copied it here with as much detail as I could capture from the Internet Archive Wayback Machine. Other than this note, the page is as I found it, and I have not edited it except to repoint the file hyperlinks to my local pages. This is a page of great historical value that should be preserved. I think Ben would approve of my posting it here.

If any files are missing, it was because they were not captured by the Wayback Machine. If you have copies, please send them to me, and I will include them here. I would very much like a copy of the source of Pierre-Andre Laurent's application if anyone has it! I have not been able to get in touch with him about it.

Lychrel Numbers

First, some definitions:

Not all numbers that fail to reach a palindrome count as Lychrel numbers, though. Many simply exist as a direct consequence of an earlier Lychrel number (such as 887, which results from 196+691=887). Others, like 295, do not themselves form part of a different Lychrel's iterations, but still join up with it at some point (295+592=887, imagine that!). So, of any given series of numbers iterated with the 196 algorithm, only the lowest number that leads to that series counts as a proper Lychrel number.

Okay, I know, you can find all of this much better explained elsewhere, and I'll give links to a few of them now (No exclusion of good web pages intended... If you think you have a page on par with one of these for quality of content, yet not totally redundant, let me know and I'll consider giving you a link)

As my contribution to the world of numerical palindromes, aside from writing a variety of useful Lychrel-related tools and holding a few current-and-past records myself, I have decided to run this 196-and-Lychrel-oriented source code repository.

Author Date Language Status Link Comments
Barry Roberts 04/27/2005 C PD?
Barry uses arbitrary-length integer routines to deal
with actual numbers, rather than strings of digits.
Matthew Stenson 09/29/2004 F90 + asm GPL2 palindrome_gui.7z
(archive includes v1)
The most recent (final?) version of Matt's iterator.
Added an assembly FAA routine for performance.
Matthew Stenson 08/30/2003 C+MMX (VS) GPL2 A port of my example code,, that
builds under Visual Studio 6 with MASM. Thanks!
Matthew Stenson 08/19/2003 Fortran 90 GPL2 palindrome_gui.7z
(archive includes v3)
The first viable F90 implementation I've
ever seen. Uses a lookup-table appproach
Eric Goldstein 03/22/2003 Inline P4 asm PD e_goldst.c The current speed-record holding
reverse-and-add implementation
Prosper & Veigneau 03/21/2003 C PD? vp_sg.c An arbitrary-base vanilla-C implementation.
Interesting optimizations, well worth studying
Benjamin Despres 10/04/2002 C GPL2 Windows GUI-mode version of the MOD-9
checker. Includes several data visualization tools
Calin A. Culianu 08/20/2002 C++ GPL2 culianu.cpp A pure C++ version, quite readable,
allows calculations in an arbitrary base
Benjamin Despres 07/26/2002 C GPL2 Verifies a save point in Istvan's file
format, usign the MOD-9 checksum
Benjamin Despres 06/28/2002 C + asm(MMX) GPL2 The once-fastest reverse-and-add code,
since superseded a few times.
David Gillies 03/15/2002 C PD? palin.c Linux version, makes use of a
digit-at-a-time lookup table
John Walker 08/1987 C PD? pquest.c The original, not all that fast,
but of unquestionable historic value

Those entries with a question mark in their status have an unknown official status, though for various reasons I assume them as released into the Public Domain. If you wrote one of these and wish it removed, contact me and I will immediately comply.

Anyone else wanting to post their source code here, please don't hesitate to contact me, though don't just send me unsolicited email attachments (your waste of time, not mine, so...). If you have my "real" email address, you can send me attachments; otherwise, email me at the address you see at the bottom of this page, and I'll reply from my real address (If I don't reply, most likely your email ended up accidentally erased in a mass spam-purging, so just try again a few days later). As I mentioned, I would recommend anyone posting source code release it under the GPL, which protects the author by defining very clear terms of use, credit, and distribution, as well as limiting liability.

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