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A159070 Count of numbers k in the range 1 < k <= n such that set of proper divisors of k is a subset of the set of proper divisors of n. 2
0, 1, 2, 3, 3, 5, 4, 6, 5, 6, 5, 10, 6, 8, 8, 9, 7, 11, 8, 12, 10, 10, 9, 16, 10, 11, 11, 13, 10, 17, 11, 15, 13, 13, 13, 19, 12, 14, 14, 19, 13, 19, 14, 18, 19, 16, 15, 24, 16, 19, 17, 19, 16, 22, 18, 23, 18, 18, 17, 28, 18, 20, 23, 23, 20, 24, 19, 23, 21, 26, 20, 31, 21, 23, 25, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Here proper divisors include 1 but not the argument (k or n, respectively) in the divisor set, as defined in A032741.

LINKS

Table of n, a(n) for n=1..76.

FORMULA

a(n) = A158973(n) - 1.

If p = prime, element of A000040, a(p) = A158973(p) - 1 = A036234(p) - 1 = A000720(p).

EXAMPLE

a(8) = 6 admits the following 6 k: 2 {1}, 3 {1}, 4 {1, 2}, 5 {1}, 7 {1}, 8 {1, 2, 4} with subsets of the proper divisors {1, 2, 4} for n = 8.

CROSSREFS

Cf. A158973, A000040, A036234, A000720.

Sequence in context: A086898 A123031 A271709 * A088241 A163126 A304818

Adjacent sequences:  A159067 A159068 A159069 * A159071 A159072 A159073

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Apr 04 2009

EXTENSIONS

Edited and extended by R. J. Mathar, Apr 06 2009

STATUS

approved

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Last modified July 3 06:54 EDT 2022. Contains 355031 sequences. (Running on oeis4.)