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 A231155 #38 Dec 09 2014 03:35:43 %S A231155 9,88,999,9999,77777,999999,9999999,88888888,999999999,9999999999, %T A231155 77777777777,999999999999,9999999999999,88888888888888, %U A231155 999999999999999,9999999999999999,77777777777777777,999999999999999999,9999999999999999999 %N A231155 Largest k such that no sum of digits is divisible by n (zeros not allowed in the digits of k). %C A231155 a(n) has fewer than n digits, a special case of the fact that n integers always contain a sub(multi)set with a sum divisible by n. %C A231155 The single digits appear to be periodic with period 210. - _T. D. Noe_, Nov 05 2013 %C A231155 This follows from the formula. Note also that the only digits which appear are 1, 5, 7, 8, and 9. - _Charles R Greathouse IV_, Nov 06 2013 %F A231155 a(n) consists of n-1 digits of d where d is the largest digit such that GCD(n,d)=1. %F A231155 a(n) = A231470(n)*(10^(n-1)-1)/9. - _M. F. Hasler_, Nov 09 2013 %e A231155 a(4) = 999 because none of 9, 9+9 or 9+9+9 are divisible by 4. All integers greater than 999 (with no zeros) have the property that some digit sum is divisible by 4, e.g., 1235 has 3+1. %o A231155 (PARI) a(n)=forstep(k=9,1,-1,if(gcd(n,k)==1, return(10^(n-1)\9*k))) \\ _Charles R Greathouse IV_, Nov 05 2013 %Y A231155 Subsequence of A010785. %K A231155 nonn,base,easy %O A231155 2,1 %A A231155 _Jon Perry_, Nov 04 2013 %E A231155 a(9)-a(20) from _Charles R Greathouse IV_, Nov 05 2013