

A317443


a(n) = number of k with 1 <= k <= n1 such that a(k) + a(nk) is not squarefree.


3



0, 1, 0, 2, 0, 3, 0, 7, 0, 7, 0, 10, 0, 9, 2, 8, 4, 9, 8, 10, 8, 11, 10, 17, 8, 13, 12, 15, 4, 19, 4, 25, 6, 17, 8, 25, 12, 19, 10, 27, 10, 23, 14, 22, 16, 25, 16, 26, 12, 21, 16, 22, 14, 31, 16, 40, 14, 29, 20, 32, 14, 27, 22, 35, 24, 33, 24, 32, 28, 25, 18
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,4


COMMENTS

We consider that 0 is not squarefree.
The scatterplot of the sequence has stripes linked to the 2adic valuation of n.


LINKS



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, n1, !issquarefree(a[k]+a[nk])); print1 (a[n] ", "))


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



