A129287 - OEIS

%I #10 Jan 27 2021 05:35:24

%S 29,30,31,29,30,28,29,30,30,29,28,28,29,30,30,29,29,28,30,30,31,29,29,

%T 28,29,30,30,29,28,28,29,30,31,29,29,28,30,30,30,29,29,28,29,30,30,29,

%U 28,28,30,30,31,29,29,28,29,30,30,29,29,28,29,30,30,29,29,28,30,30,31

%N Number of Harshad numbers between 10^n and 10^n + 100.

%C Will every term be between 28 and 31 inclusive?

%D Jason Earls, Red Zen, Lulu Press, NY, 2006, pp. 145-146. ISBN: 978-1-4303-2017-3.

%H Amiram Eldar, <a href="/A129287/b129287.txt">Table of n, a(n) for n = 3..10000</a>

%e There are exactly 29 Harshad numbers between 1000 and 1100, so the first term is 29.

%t a[n_] := Count[Range[10^n, 10^n + 100], _?(Divisible[#, Plus @@ IntegerDigits[#]] &)]; Array[a, 70, 3] (* _Amiram Eldar_, Jan 27 2021 *)

%Y Cf. A005349.

%K nonn,base

%O 3,1

%A _Jason Earls_, May 26 2007