

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
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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*d1] `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



