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A056676 Number of non-unitary but squarefree divisors of binomial(n,floor(n/2)). Also number of nonsquarefree but unitary divisors of binomial(n,floor(n/2)). 0
0, 0, 0, 0, 0, 2, 0, 0, 4, 6, 0, 8, 8, 8, 8, 16, 0, 16, 0, 16, 32, 32, 0, 32, 48, 48, 56, 56, 96, 96, 64, 128, 128, 192, 256, 384, 384, 384, 512, 768, 512, 512, 512, 512, 448, 448, 768, 896, 896, 896, 896, 896, 768, 768, 2048, 2048, 4096, 4096, 2048, 2048, 2048, 2048 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..62.

FORMULA

a(n) = A039593(n) - A000005(A055231(x)) = A039593(n) - A000005(A007913(x)/A055229(x)), where x = A001405(n) = binomial(n, floor(n/2)).

EXAMPLE

n=14, C(14,7)=3432, has 32 divisors, 16 unitary, 16 squarefree. The size of overlap is 8. The complementary parts are: non-unitary/squarefree set={2,6,22,26,66,78,286,828}, while the unitary/not squarefree set of equal size is {8,24,88,104,264,312,1144,3432}. So a(14)=8.

CROSSREFS

Cf. A039593, A000005, A055231, A007913, A055229, A001405.

Sequence in context: A244138 A284611 A282551 * A098699 A021837 A236934

Adjacent sequences:  A056673 A056674 A056675 * A056677 A056678 A056679

KEYWORD

nonn

AUTHOR

Labos Elemer, Aug 10 2000

STATUS

approved

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Last modified November 19 18:39 EST 2019. Contains 329323 sequences. (Running on oeis4.)