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%I #16 Mar 08 2018 21:14:12
%S 1,10,11,19,38,46,47,56,57,65,73,74,83,84,92,100,101,110,111,119,138,
%T 145,155,163,164,172,182,190,191,209,218,228,236,237,245,255,263,264,
%U 272,282,289,299,308,316,317,326,327,335,343,344,353,354,362,380,381
%N Numbers n such that the digit sum of n*7 is a multiple of 7.
%C If n is in the sequence, so are 10*n and 10*n+1. - _Robert Israel_, Mar 08 2018
%H Robert Israel, <a href="/A216996/b216996.txt">Table of n, a(n) for n = 1..10000</a>
%e 7*19 = 133 and 1+3+3=7.
%p filter:= n -> convert(convert(7*n,base,10),`+`) mod 7 = 0:
%p select(filter, [$1..1000]); # _Robert Israel_, Mar 08 2018
%t Select[Range[500], Mod[Total[IntegerDigits[7*#]], 7] == 0 &] (* _T. D. Noe_, Sep 24 2012 *)
%o (JavaScript)
%o function sumarray(arr) {
%o t=0;
%o for (i=0;i<arr.length;i++) t+=arr[i];
%o return t;
%o }
%o k=7;
%o for(s=1;s<1000;s++) {
%o a=new Array();
%o x=(s*k).toString();
%o for (j=0;j<x.length;j++) a[j]=Number(x.charAt(j));
%o if (sumarray(a)%k==0) document.write(s+",");
%o }
%Y Cf. A216994, A216995, A216997, A216998, A217009.
%K nonn,base
%O 1,2
%A _Jon Perry_, Sep 22 2012
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