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 A316312 Numbers k such that the sum of the digits of the numbers 1, 2, 3, ... up to (k - 1) is divisible by k. 1
 1, 3, 5, 7, 9, 12, 15, 20, 27, 40, 45, 60, 63, 80, 81, 100, 180, 181, 300, 360, 363, 500, 540, 545, 700, 720, 727, 900, 909, 912, 915, 1137, 1140, 1200, 1500, 1560, 1563, 2000, 2700, 2720, 2727, 4000, 4500, 4540, 4545, 6000, 6300, 6360, 6363, 8000, 8100, 8180 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers k such that A007953(A007908(k - 1)) is divisible by k. - Felix Fröhlich, Jun 29 2018 From Robert Israel, Jun 29 2018: (Start) Numbers k such that A037123(k - 1) is divisible by k. If m is even, then 10^m, 3 * 10^m, 5 * 10^m, 7 * 10^m and 9 * 10^m are included. If m is odd, then 2 * 10^m, 4 * 10^m, 6 * 10^m, and 8 * 10^m are included. (End) Is it true that if k is a term then 100 * k is a term? LINKS Henry Bottomley, Table of n, a(n) for n = 1..118 EXAMPLE For n = 7, sum of the digits of the numbers 1 to 6 is 21, which is divisible by 7. For n = 12, sum of the digits of the numbers 1 to 11 is 48, which is divisible by 12. For n = 15, sum of the digits of the numbers 1 to 14 is 60, which is divisible by 15. 16 is not in the sequence because the sum of the digits of the numbers 1 to 15 is 66, which is not divisible by 16. MAPLE t:= 0: Res:= NULL: for n from 1 to 10000 do t:= t + convert(convert(n-1, base, 10), `+`); if (t/n)::integer then Res:= Res, n fi od: Res; # Robert Israel, Jun 29 2018 MATHEMATICA s = 0; Reap[Do[If[Mod[s, n] == 0, Sow[n]]; s += Plus @@ IntegerDigits@n, {n, 10000}]][[2, 1]] (* Giovanni Resta, Jun 29 2018 *) PROG (PARI) sumsod(n) = sum(i=1, n, sumdigits(i)) is(n) = sumsod(n-1)%n==0 \\ Felix Fröhlich, Jun 29 2018 (PARI) upto(n) = my(s=0, res=List()); for(i=0, n, s += vecsum(digits(i)); if(s%(i+1)==0, listput(res, i+1))); res \\ David A. Corneth, Jun 29 2018 CROSSREFS Cf. A007953, A007908, A037123, A110740, A114136. Sequence in context: A226332 A226331 A333601 * A362128 A118015 A265057 Adjacent sequences: A316309 A316310 A316311 * A316313 A316314 A316315 KEYWORD nonn,base AUTHOR Debapriyay Mukhopadhyay, Jun 29 2018 EXTENSIONS More terms from Felix Fröhlich, Jun 29 2018 STATUS approved

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Last modified May 24 22:09 EDT 2024. Contains 372782 sequences. (Running on oeis4.)