login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056595 Number of nonsquare divisors of n. 17
0, 1, 1, 1, 1, 3, 1, 2, 1, 3, 1, 4, 1, 3, 3, 2, 1, 4, 1, 4, 3, 3, 1, 6, 1, 3, 2, 4, 1, 7, 1, 3, 3, 3, 3, 5, 1, 3, 3, 6, 1, 7, 1, 4, 4, 3, 1, 7, 1, 4, 3, 4, 1, 6, 3, 6, 3, 3, 1, 10, 1, 3, 4, 3, 3, 7, 1, 4, 3, 7, 1, 8, 1, 3, 4, 4, 3, 7, 1, 7, 2, 3, 1, 10, 3, 3, 3, 6, 1, 10, 3, 4, 3, 3, 3, 9, 1, 4, 4, 5, 1, 7, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

a(A000430(n))=1; a(A030078(n))=2; a(A030514(n))=2; a(A006881(n))=3; a(A050997(n))=3; a(A030516(n))=3; a(A054753(n))=4; a(A000290(n))=A055205(n). - Reinhard Zumkeller, Aug 15 2011

LINKS

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

FORMULA

a(n) = A000005(n) - A046951(n) = tau(n) - tau(A000188(n)).

EXAMPLE

a(36)=5 because the set of divisors of 36 has tau(36)=nine elements, {1, 2, 3, 4, 6, 9, 12, 18, 36}, five of which, that is {2, 3, 6, 12, 18}, are not perfect squares.

MATHEMATICA

Table[Count[Divisors[n], _?(#!=Floor[Sqrt[#]]^2&)], {n, 110}] (* Harvey P. Dale, Jul 10 2013 *)

PROG

(Haskell)

a056595 n = length [d | d <- [1..n], mod n d == 0, a010052 d == 0]

-- Reinhard Zumkeller, Aug 15 2011

(PARI) a(n)=sumdiv(n, d, !issquare(d)) \\ Charles R Greathouse IV, Aug 28 2016

CROSSREFS

Cf. A000005, A000188, A046951.

See A194095 and A194096 for record values and where they occur.

Sequence in context: A157520 A227339 A030777 * A160097 A252477 A029351

Adjacent sequences:  A056592 A056593 A056594 * A056596 A056597 A056598

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 21 2000

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 19 11:05 EST 2018. Contains 317350 sequences. (Running on oeis4.)