A147827 - OEIS

%I #13 Mar 21 2016 03:13:28

%S 0,7,34,133,997,7999,13333,85714,749986,1111111,79999999,79090909,

%T 499999999,2923076923,14285642857,133333333333,499999999993,

%U 2352941117647,11111111111111,47368421052631,3499999999999999,2380947619047619,25909090909090909,43478260869565213

%N Minimum number k for which the digital sum of k*n is 7*n.

%H Chai Wah Wu, <a href="/A147827/b147827.txt">Table of n, a(n) for n = 0..27</a>

%p P:=proc(i) local j,k,n,ok,w; for n from 0 by 1 to i do j:=-1; ok:=1; while ok=1 do j:=j+1; w:=0; k:=n*j; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if w=7*n then ok:=0; print(j); fi; od; od; end: P(100);

%o (PARI) a(n) = {my(k = 0); while (sumdigits(k*n) != 7*n, k++); k;}; \\ _Michel Marcus_, Mar 21 2016

%Y Cf. A147822-A147826, A147828-A147831.

%K easy,nonn,base

%O 0,2

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Nov 14 2008

%E Edited by _Charles R Greathouse IV_, Nov 01 2009

%E a(9)-a(16) from _Donovan Johnson_, Sep 16 2012

%E a(17)-a(23) from _Chai Wah Wu_, Mar 20 2016