Oh, yes, Neil, thanks !-)) I'm computing by hand this one: "The digital root of a(n) is the digital root of the sum of the a(n) first terms": 1,3,8,9,10,11,12,17,19,28,38,... Best, E. -------- Message d'origine-------- De: math-fun-bounces@mailman.xmission.com de la part de N. J. A. Sloane Date: jeu. 25/02/2010 23:58 À: math-fun@mailman.xmission.com Objet : Re: [math-fun] What is the name of [mod 9 digitsum] Eric, maybe you have heard of the OEIS? The OEIS is designed to identify a sequence of numbers! You would find this: %I A010888 %S A010888 0,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7, %T A010888 8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6, %U A010888 7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,1,2,3,4,5 %N A010888 Digital root of n (repeatedly add digits until reach a single digit). .... Cheers! Neil _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun