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A005349 Niven (or Harshad) numbers: numbers that are divisible by the sum of their digits.
(Formerly M0481)

%I M0481

%S 1,2,3,4,5,6,7,8,9,10,12,18,20,21,24,27,30,36,40,42,45,48,50,54,60,63,

%T 70,72,80,81,84,90,100,102,108,110,111,112,114,117,120,126,132,133,

%U 135,140,144,150,152,153,156,162,171,180,190,192,195,198,200,201,204

%N Niven (or Harshad) numbers: numbers that are divisible by the sum of their digits.

%C z-Niven numbers are numbers n which are divisible by (A*s(n) + B) where A, B are integers and s(n) is sum of digits of n. Niven numbers have A = 1, B = 0. - _Ctibor O. Zizka_, Feb 23 2008

%C A070635(a(n)) = 0. A038186 is a subsequence. - _Reinhard Zumkeller_, Mar 10 2008

%C A049445 is a subsequence of this sequence. - _Ctibor O. Zizka_, Sep 06 2010

%C Complement of A065877; A188641(a(n)) = 1; A070635(a(n)) = 0. - _Reinhard Zumkeller_, Apr 07 2011

%C A001101, the Moran numbers, are a subsequence. - _Reinhard Zumkeller_, Jun 16 2011

%C A140866 gives the number of terms <= 10^k. - _Robert G. Wilson v_, Oct 16 2012

%D Paul Dahlenberg and T. Edgar, Consecutive factorial base Niven numbers, Fib. Q., 56:2 (2018), 163-166.

%D R. E. Kennedy and C. N. Cooper, On the natural density of the Niven numbers, Abstract 816-11-219, Abstracts Amer. Math. Soc., 6 (1985), 17.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%D D. Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, 171.

%H N. J. A. Sloane, <a href="/A005349/b005349.txt">Table of n, a(n) for n = 1..11872</a> (all a(n) <= 100000)

%H C. N. Cooper, R. E. Kennedy, <a href="http://www.jstor.org/stable/2323194">Chebyshev's inequality and natural density</a>, Amer. Math. Monthly 96 (1989), no. 2, 118-124.

%H Jean-Marie De Koninck and Nicolas Doyon, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL6/Doyon/doyon.html">Large and Small Gaps Between Consecutive Niven Numbers</a>, J. Integer Seqs., Vol. 6, 2003, Article 03.2.5.

%H R. K. Guy, <a href="http://www.jstor.org/stable/2691503">The Second Strong Law of Small Numbers</a>, Math. Mag, 63 (1990), no. 1, 3-20.

%H R. K. Guy, <a href="/A005347/a005347.pdf">The Second Strong Law of Small Numbers</a>, Math. Mag, 63 (1990), no. 1, 3-20. [Annotated scanned copy]

%H R. E. Kennedy, <a href="http://www.trottermath.net/numthry/nivennos.html">Niven Numbers for Fun and Profit</a> [Warning: As of March 2018 this site appears to have been hacked. Proceed with great caution. The original content should be retrieved from the Wayback machine and added here. - _N. J. A. Sloane_, Mar 29 2018]

%H R. E. Kennedy and C. N. Cooper, <a href="http://www.jstor.org/stable/2686395">On the natural density of the Niven numbers</a>, The College Mathematics Journal, Vol. 15, No. 4 (Sep., 1984), pp. 309-312.

%H Project Euler, <a href="http://projecteuler.net/problem=387">Harshard Numbers: Problem 387</a>

%H GĂ©rard Villemin, <a href="http://villemin.gerard.free.fr/Wwwgvmm/Decompos/Harshad.htm">Nombres de Harshad</a> (French)

%H Elaine E. Visitacion, Renalyn T. Boado, Mary Ann V. Doria, Eduard M. Albay, <a href="http://www.dmmmsu-sluc.com/wp-content/uploads/2018/03/CAS-Monitor-2016-2017-1.pdf">On Harshad Number</a>, DMMMSU-CAS Science Monitor (2016-2017) Vol. 15 No. 2, 134-138.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Digit.html">Digit</a> and <a href="http://mathworld.wolfram.com/HarshadNumber.html">Harshad Numbers</a>

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Harshad_number">Harshad number</a>

%e 195 is a term of the sequence because it is divisible by 15 (= 1 + 9 + 5).

%p s:=proc(n) local N:N:=convert(n,base,10):sum(N[j],j=1..nops(N)) end:p:=proc(n) if floor(n/s(n))=n/s(n) then n else fi end: seq(p(n),n=1..210); # _Emeric Deutsch_

%t harshadQ[n_] := Mod[n, Plus @@ IntegerDigits@ n] == 0; Select[ Range[1000], harshadQ] (* _Alonso del Arte_, Aug 04 2004 and modified by _Robert G. Wilson v_, Oct 16 2012 *)

%t Select[Range[300],Divisible[#,Total[IntegerDigits[#]]]&] (* _Harvey P. Dale_, Sep 07 2015 *)

%o (Haskell)

%o a005349 n = a005349_list !! (n-1)

%o a005349_list = filter ((== 0) . a070635) [1..]

%o -- _Reinhard Zumkeller_, Aug 17 2011, Apr 07 2011

%o (MAGMA) [n: n in [1..250] | n mod &+Intseq(n) eq 0]; // _Bruno Berselli_, May 28 2011

%o (MAGMA) [n: n in [1..250] | IsIntegral(n/&+Intseq(n))]; // _Bruno Berselli_, Feb 09 2016

%o (PARI) is(n)=n%sumdigits(n)==0 \\ _Charles R Greathouse IV_, Oct 16 2012

%o (Python)

%o A005349 = [n for n in range(1,10**6) if not n % sum([int(d) for d in str(n)])] # _Chai Wah Wu_, Aug 22 2014

%Y Cf. A001101, A007602, A007953, A028834, A038186, A049445, A052018, A052019, A052020, A052021, A052022, A065877, A070635, A113315, A188641.

%Y Cf. A001102 (a subsequence).

%Y Cf. A118363 (for factorial-base analog).

%K nonn,base,nice,easy

%O 1,2

%A _N. J. A. Sloane_, _Robert G. Wilson v_

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Last modified July 22 10:45 EDT 2018. Contains 312891 sequences. (Running on oeis4.)