Playing with c = (a*b) mod (a+b)

[Eric Angelini]

Thanks to Chuck, Jack and Maximilian :
http://www.cetteadressecomportecinquantesignes.com/ModuloPlay.htm
Best,
É.


-----Message d'origine-----
De : Eric Angelini [mailto:Eric.Angelini at kntv.be] 
Envoyé : lundi 7 juillet 2008 19:03
À : math-fun; seqfan at ext.jussieu.fr
Objet : Playing with c = (a*b) mod (a+b)


Hello MathFun & SeqFans,

  Start S = 2, 9,...

Next term is (2*9)mod(2+9)
               18 mod 11 = 7
  S = 2, 9, 7,...

Next term is (9*7)mod(9+7)
               63 mod 16 = 15
  S = 2, 9, 7, 15,...

Next term is (7*15)mod(7+15)
               105 mod 22 = 17
  S = 2, 9, 7, 15, 17,...

Next term is (15*17)mod(15+17)
               255 mod 32 = 31
  S = 2, 9, 7, 15, 17, 31,...

Next term is (17*31)mod(17+31)
               527 mod 48 = 47
 S = 2, 9, 7, 15, 17, 31, 47,...

Does this end in a loop?
If yes, is there another start
which doesn't?

Best,
É.









Dear Sequence Fans, At present the entry reads as follows:

%I A063979
%S A063979 1,1,1,3,24,199,1747,16474,168187,1859934,22228104,286078171,
%T A063979 3949867548,58284826485,915905054360,15276520209206,269617872744249,
%U A063979 5021159048900643,98417586560408168,2025488254833817394
%N A063979 Number of decimal digits in (n!)!; A000197.
%H A063979 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Factorial.html">Factorial</a>
%p A063979 seq(length((n)!!), n=0..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 10 2007
%t A063979 Do[ Print[ Floor[ N[ Log[10, (n!)! ], 24] + 1]], {n, 0, 11} ]
%Y A063979 Cf. A000197, A063944, A034886.
%K A063979 base,nonn
%O A063979 0,4
%A A063979 Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 05 2001
%E A063979 More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), Sep 06 2001

Dmitry Kamenetsky (dkamen at rsise.anu.edu.au), Jul 08 2008 says:

%C A063979 for n=17, 18 and 19 I get 5021159048900644, 98417586560408160 and 20254882548338170
88 respectively. This is slightly different to the quoted numbers. Can someone please verify t
his?

%o A063979 Here is my Python program:

from math import sqrt, pi, log, e, floor

def fact(n):


def fact2(n):



for n in xrange(1,20):

(end of quote)

Which version is correct?

Thanks
Neil