Dear SeqFans, I came across a paper, Phys. Rev. 65, 195 - 201 (1944) Ambiguities in the X-Ray Analysis of Crystal Structures by A L Patterson http://prola.aps.org/abstract/PR/v65/i5-6/p195_1 is the URL, if your institution subscribes (mine does not) In Table I there is a triangle of numbers, which the author admits he is not confident about (which is probably why I left them out of the 1973 book) I know that there have been several followup papers. It might be an interesting project for someone to look into this, determine the correct triangle(s), and submit it to the OEIS, The subject is the ways to place n points around a circle so that the set of n-choose-2 distances do/do not determine the points [Related to the classical problem, worked on by Petard, as I recall, who got it wrong - hoisted with your own Petard? - of when the distances between n points anywhere in the plane determine the pints.] Might be an interesting problem to work on (the Patterson paper, I mean). Neil