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A317443 a(n) = number of k with 1 <= k <= n-1 such that a(k) + a(n-k) 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 (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 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

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

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Last modified February 16 15:17 EST 2020. Contains 331961 sequences. (Running on oeis4.)