This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A178505 #20 Mar 19 2025 06:12:49 %S A178505 3,142857,1,9,76923,588235294117647,52631578947368421,47619, %T A178505 434782608695652173913,37,344827586206896551724137931,32258064516129, %U A178505 3,27,25641,2439,23255813953488372093 %N A178505 Decimal form of the period of 1/n for n such that gcd(n,10)=1. Leading zeros are suppressed. %C A178505 The numbers n are A045572, and the corresponding periods are A002329. %H A178505 Ray Chandler, <a href="/A178505/b178505.txt">Table of n, a(n) for n = 1..406</a> (terms up to 1000 digits) %F A178505 a(n) = A060284(A045572(n+1)). [_R. J. Mathar_, Jun 26 2010] %e A178505 3 is in the sequence because 1/3 = 0.3333... %e A178505 142857 is in the sequence because 1/7 = 0.142857 142857 ... %e A178505 1 is in the sequence because 1/9 = 0.1111.... %p A178505 with(numtheory): nn:= 100: T:=array(1..nn):k:=1: U:=array(1..nn):k:=1: for n from 2 to 200 do:x:=1/n:for p from 1 to 200 while(irem(10^p,n)<>1 or gcd(n,10)<> 1) do:od: if irem(10^p,n) = 1 and gcd(n,10) = 1 then y:=floor(x*10^p): T[k]:=y: U[k]:=n : k:=k+1:else fi:od:print(T): %Y A178505 Cf. A002329, A036275, A045572, A060284. %K A178505 nonn,base %O A178505 1,1 %A A178505 _Michel Lagneau_, May 29 2010 %E A178505 Name corrected by _T. D. Noe_, Jul 07 2010