%I A055272
%S A055272 1,6,42,294,2058,14406,100842,705894,4941258,34588806,242121642,
%T A055272 1694851494,11863960458,83047723206,581334062442,4069338437094,
%U A055272 28485369059658,199397583417606,1395783083923242,9770481587462694
%N A055272 First differences of 7^n (A000420).
%C A055272 Partial sum of A055270.
%C A055272 Conjecture in "Introduction a la theorie des nombres" by d'Armel Mercier 
               and J. M. Deconinck: this is the period length of the fraction 1/
               7^n. For example 1/7^2=0.0204081632653061224489795918367346938775510204....with 
               a period of 42 digits =6*7=a(2). The period of 1/7^3 has exactly 
               294=a(3) digits. - Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 
               02 2002
%C A055272 Also phi(7^n), where phi is Euler's totient function. - Alonso Delarte 
               (alonso.delarte(AT)gmail.com), May 08 2006
%C A055272 For n>=1, a(n) is equal to the number of functions f:{1,2...,n}->{1,2,
               3,4,5,6,7} such that for a fixed x in {1,2,...,n} and a fixed y in 
               {1,2,3,4,5,6,7} we have f(x)<>y. - Aleksandar M. Janjic and Milan 
               R. Janjic (agnus(AT)blic.net), Mar 27 2007
%D A055272 A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, 
               pps. 194-196.
%H A055272 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas 
               for Some Functions on Finite Sets</a>
%F A055272 a(n)=6*7^(n-1), a(0)=1.
%e A055272 a(n)=7a(n-1)+[(-1)^n]*C(1,1-n). G.f.(x)=(1-x)/(1-7x).
%t A055272 Table[EulerPhi[7^n], {n, 0, 19}] - Alonso Delarte (alonso.delarte(AT)gmail.com), 
               May 08 2006
%Y A055272 Cf. A000420 and A055270.
%Y A055272 Sequence in context: A057089 A110711 A156361 this_sequence A155196 A147838 
               A127628
%Y A055272 Adjacent sequences: A055269 A055270 A055271 this_sequence A055273 A055274 
               A055275
%K A055272 easy,nonn
%O A055272 0,2
%A A055272 Barry E. Williams, May 28 2000
%E A055272 More terms from James A. Sellers (sellersj(AT)math.psu.edu), May 30 2000