

A317443


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


2



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


CROSSREFS

Cf. A007814, A013929, A317420.
Sequence in context: A331176 A076563 A163974 * A308218 A067165 A079981
Adjacent sequences: A317440 A317441 A317442 * A317444 A317445 A317446


KEYWORD

nonn


AUTHOR

Rémy Sigrist, Jul 28 2018


STATUS

approved



