Ok, crystal clear explanations, thanks a lot, David ! I'll check tonight the three seq and send them tomorrow to the OEIS if ok ! Best, É. -----Message d'origine----- De : math-fun-bounces+eric.angelini=kntv.be@mailman.xmission.com [mailto:math-fun-bounces+eric.angelini=kntv.be@mailman.xmission.com] De la part de David Wilson Envoyé : vendredi 17 août 2007 13:47 À : math-fun Objet : Re: [math-fun] Golomb rulers An n-mark Golomb ruler has a unique integer distance between any pair of marks, and thus measures n(n-1)/2 distinct integer distances. An optimal n-mark Golomb rulers has the smallest possible length (distance between the two end marks) for an n-mark ruler. A perfect n-mark Golomb ruler has length exactly n(n-1)/2, and measures each distance from 1 to n(n-1)/2. ----- Original Message ----- From: "Eric Angelini" <Eric.Angelini@kntv.be> To: "math-fun" <math-fun@mailman.xmission.com> Sent: Friday, August 17, 2007 6:31 AM Subject: [math-fun] Golomb rulers Hello, ... I am confused, having just read this on Eric Weisstein site: "However, the unique optimal Golomb 4-mark ruler is (0, 1, 4, 6), which measures the distances (1, 2, 3, 4, 5, 6) (and is therefore also a perfect ruler). As a further example, it turns out that the length of an optimal 6-mark Golomb ruler is 17. In fact, there are a total of four distinct 6-mark Golomb rulers, all of length 17, one of which is given by (0, 1, 4, 10, 12, 17). " http://mathworld.wolfram.com/GolombRuler.html ... What is the difference between a "perfect ruler" and an "optimal ruler" ?! ... I cannot measure 14 or 15 with (0, 1, 4, 10, 12, 17) Best, É. _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.11.19/956 - Release Date: 8/16/2007 9:48 AM _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun