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A242627 Number of divisors of n that are less than 10.

%I A242627 #28 Dec 13 2021 08:05:51
%S A242627 9,1,2,2,3,2,4,2,4,3,3,1,5,1,3,3,4,1,5,1,4,3,2,1,6,2,2,3,4,1,5,1,4,2,
%T A242627 2,3,6,1,2,2,5,1,5,1,3,4,2,1,6,2,3,2,3,1,5,2,5,2,2,1,6,1,2,4,4,2,4,1,
%U A242627 3,2,4,1,7,1,2,3,3,2,4,1,5,3,2,1,6,2
%N A242627 Number of divisors of n that are less than 10.
%C A242627 Number of numbers <= 9, dividing n;
%C A242627 a(n) <= 9; a(2520*n) = 9;
%C A242627 a(n) = (number of repdigit numbers in row n of triangle A242614) = sum(A202022(A242614(n,k)): k=1..A242622(n)), for n > 0.
%C A242627 Periodic with period 2520. Each period there are 576 1's, 720 2's, 464 3's, 360 4's, 206 5's, 122 6's, 58 7's, 13 8's, and 1 9 (average 2.82...). - _Charles R Greathouse IV_, Sep 27 2015
%H A242627 Reinhard Zumkeller, <a href="/A242627/b242627.txt">Table of n, a(n) for n = 0..10000</a>
%H A242627 <a href="/index/Rec#order_28">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-4,-7,-11,-15,-20,-24,-27,-28,-27,-23,-17,-9,0,9,17,23,27,28,27,24,20,15,11,7,4,2,1).
%F A242627 G.f.: Sum_(j=1..9, 1/(1-x^j)). - _Robert Israel_, Jul 31 2014
%p A242627 a:= n -> numboccur(0,map2(`modp`,n,[$1..9])):
%p A242627 map(a,[$0..100]); # _Robert Israel_, Jul 31 2014
%t A242627 a[n_] := If[n == 0, 9, Count[Divisors[n], d_ /; d < 10]];
%t A242627 Table[a[n], {n, 0, 100}] (* _Jean-François Alcover_, Dec 13 2021 *)
%o A242627 (Haskell)
%o A242627 a242627 n = length $ filter ((== 0) . mod n) [1..9]
%o A242627 (PARI) a(n)=1+sum(k=2,9,n%k<1) \\ _Zak Seidov_, Jul 31 2014
%Y A242627 Cf. A165412.
%K A242627 nonn,easy
%O A242627 0,1
%A A242627 _Reinhard Zumkeller_, Jul 16 2014