OFFSET
1,6
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Benoit Cloitre, Graph of a(n) for n=1 up to 25
Benoit Cloitre, Graph of a(n) for n=1 up to 125
Benoit Cloitre, Graph of a(n) for n=1 up to 625
FORMULA
a(1) = 0, then a(n) = w(n) - a(n-w(n)) where w(n) = 5^floor(log(n-1)/log(5)).
a(n) = Sum_{i=1..n-1} (-1)^(i-1)*5^valuation(i, 5).
Conjecture: a(n+1) = (n mod 2) + Sum_{k=0..infinity} (4*5^k*(floor(n/5^(k+1)) mod 2)). - Charlie Neder, May 25 2019
MATHEMATICA
a[n_] := Sum[(-1)^(i+1) * 5^IntegerExponent[i, 5], {i, 1, n-1}]; Array[a, 100] (* Amiram Eldar, Jun 17 2022 *)
PROG
(PARI) a(n)=if(n<2, 0, 5^floor(log(n-1)/log(5))-a(n-5^floor(log(n-1)/log(5))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Apr 26 2004
STATUS
approved