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A216996 Numbers n such that the digit sum of n*7 is a multiple of 7. 6
1, 10, 11, 19, 38, 46, 47, 56, 57, 65, 73, 74, 83, 84, 92, 100, 101, 110, 111, 119, 138, 145, 155, 163, 164, 172, 182, 190, 191, 209, 218, 228, 236, 237, 245, 255, 263, 264, 272, 282, 289, 299, 308, 316, 317, 326, 327, 335, 343, 344, 353, 354, 362, 380, 381 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If n is in the sequence, so are 10*n and 10*n+1. - Robert Israel, Mar 08 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

7*19 = 133 and 1+3+3=7.

MAPLE

filter:= n -> convert(convert(7*n, base, 10), `+`) mod 7 = 0:

select(filter, [$1..1000]); # Robert Israel, Mar 08 2018

MATHEMATICA

Select[Range[500], Mod[Total[IntegerDigits[7*#]], 7] == 0 &] (* T. D. Noe, Sep 24 2012 *)

PROG

(JavaScript)

function sumarray(arr) {

t=0;

for (i=0; i<arr.length; i++) t+=arr[i];

return t;

}

k=7;

for(s=1; s<1000; s++) {

a=new Array();

x=(s*k).toString();

for (j=0; j<x.length; j++) a[j]=Number(x.charAt(j));

if (sumarray(a)%k==0) document.write(s+", ");

}

CROSSREFS

Cf. A216994, A216995, A216997, A216998, A217009.

Sequence in context: A225079 A214790 A191221 * A165265 A197652 A261909

Adjacent sequences:  A216993 A216994 A216995 * A216997 A216998 A216999

KEYWORD

nonn,base

AUTHOR

Jon Perry, Sep 22 2012

STATUS

approved

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Last modified September 22 08:23 EDT 2018. Contains 315270 sequences. (Running on oeis4.)