A218447 - OEIS

%I #19 Apr 30 2021 10:57:44

%S 0,0,0,0,1,1,1,1,2,3,3,3,4,4,5,5,6,6,7,8,9,9,9,9,11,11,11,12,14,15,15,

%T 15,16,16,17,17,19,19,20,21,22,22,23,23,25,26,26,26,28,29,29,29,30,30,

%U 32,32,34,35,36,37,38,38,38,39,41,41,41,41,43,44,45,45,48,48,49,49,51,51,52,53,54

%N a(n) = Sum_{k>=0} floor(n/(5*k + 4)).

%C Partial sums of A001899.

%H Robert Israel, <a href="/A218447/b218447.txt">Table of n, a(n) for n = 0..10000</a>

%p g:= n -> nops(select(t -> t mod 5 = 4, numtheory:-divisors(n))):

%p g(0):= 0:

%p ListTools:-PartialSums(map(g, [$0..100])); # _Robert Israel_, Apr 29 2021

%o (PARI) a(n)=sum(k=0,n,(n\(5*k+4)))

%o (Maxima) A218447[n]:=sum(floor(n/(5*k+4)),k,0,n)$

%o makelist(A218447[n],n,0,80); /* _Martin Ettl_, Oct 20 2012 */

%Y Cf. A001899

%K nonn

%O 0,9

%A _Benoit Cloitre_, Oct 28 2012