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A174903 Number of divisors d of n such that d<e<2*d for at least another divisor e of n. 5
0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 3, 0, 0, 1, 0, 0, 2, 0, 1, 0, 0, 0, 5, 0, 0, 0, 1, 0, 5, 0, 0, 0, 0, 1, 6, 0, 0, 0, 3, 0, 3, 0, 0, 3, 0, 0, 7, 0, 0, 0, 0, 0, 3, 0, 3, 0, 0, 0, 9, 0, 0, 1, 0, 0, 3, 0, 0, 0, 3, 0, 9, 0, 0, 2, 0, 1, 2, 0, 5, 0, 0, 0, 9, 0, 0, 0, 1, 0, 9, 1, 0, 0, 0, 0, 9, 0, 0, 1, 2, 0, 2, 0, 1, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,12

COMMENTS

a(A174905(n)) = 0; a(A005279(n)) > 0;

a(A174904(n)) = n and a(m) <> n for m < A174904(n);

a(m)*a(n) <= a(m)*a(n) for m, n coprime.

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

a(12) = #{(2,3), (3,4), (4,6)} = 3;

a(15) = #{(3,5)} = 1;

a(18) = #{(2,3), (6,9)} = 2;

a(20) = #{(4,5)} = 1;

a(24) = #{(2,3), (3,4), (4,6), (6,8), (8,12)} = 5.

PROG

(Haskell)

import Data.List (intersect)

a174903 n = length [d | let ds = a027750_row n, d <- ds,

not $ null [e | e <- [d+1 .. 2*d-1] `intersect` ds]]

-- Reinhard Zumkeller, Sep 29 2014

CROSSREFS

Cf. A000005, A005279, A174904, A174905.

Sequence in context: A186038 A091009 A204814 * A167163 A005890 A104515

Adjacent sequences: A174900 A174901 A174902 * A174904 A174905 A174906

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Apr 01 2010

STATUS

approved

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Last modified December 2 07:06 EST 2022. Contains 358493 sequences. (Running on oeis4.)