OFFSET
1,4
COMMENTS
We consider that 0 is not squarefree.
The scatterplot of the sequence has stripes linked to the 2-adic valuation of n.
See A317420 for similar sequences.
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10000
Rémy Sigrist, Colored scatterplot of the first 1000000 terms (where the color is function of A007814(n))
EXAMPLE
For n = 4:
- a(1) + a(3) = 0 + 0 = 0 is not squarefree,
- a(2) + a(2) = 1 + 1 = 2 is squarefree,
- a(3) + a(1) = 0 + 0 = 0 is not squarefree,
- hence a(4) = 2.
PROG
(PARI) a = vector(71); for (n=1, #a, a[n] = sum(k=1, n-1, !issquarefree(a[k]+a[n-k])); print1 (a[n] ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Jul 28 2018
STATUS
approved