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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A129510 Number of distinct differences between pairs of distinct divisors of n. 6
0, 1, 1, 3, 1, 5, 1, 6, 3, 6, 1, 10, 1, 6, 5, 10, 1, 13, 1, 13, 6, 6, 1, 18, 3, 6, 6, 14, 1, 19, 1, 15, 6, 6, 6, 24, 1, 6, 6, 22, 1, 23, 1, 15, 12, 6, 1, 30, 3, 15, 6, 15, 1, 25, 6, 23, 6, 6, 1, 37, 1, 6, 13, 21, 6, 25, 1, 15, 6, 24, 1, 40, 1, 6, 13, 15, 6, 26, 1, 34, 10, 6, 1, 45, 6, 6, 6, 26 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = #{|x-y|: x <> y and n mod x = n mod y = 0};

a(n) = 1 iff n is prime;

a(n) <= A000217(A000005(a(n))-1) = A066446(n):

a(A129511(n))=A066446(A129511(n)), a(A129512(n)) < A066446(A129512(n)).

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Divisor

EXAMPLE

n=44, set of divisors of 44 = {1,2,4,11,22,44}:

44-22=22, 44-11=33, 44-4=40, 44-2=42, 44-1=41,

22-11=11, 22-4=18, 22-2=20, 22-1=21,

11-4=7, 11-2=9, 11-1=10, 4-2=2, 4-1=3, 2-1=1,

a(44) = #{1,2,3,7,9,10,11,18,20,21,22,33,40,41,42} = 15;

n=45, set of divisors of 45 = {1,3,5,9,15,45}:

45-15=30, 45-9=36, 45-5=40, 45-3=42, 45-1=44,

15-9=6, 15-5=10, 15-3=12, 15-1=14,

9-5=4, 9-3=6, 9-1=8, 5-3=2, 5-1=4, 3-1=2,

a(45) = #{2,4,6,8,10,12,14,30,36,40,42,44} = 12.

PROG

(PARI) a(n)=my(d=divisors(n), v=List()); for(i=1, #d-1, for(j=i+1, #d, listput(v, d[j]-d[i]))); #Set(v) \\ Charles R Greathouse IV, Aug 26 2015

CROSSREFS

Cf. A000005.

Sequence in context: A002972 A029652 A238952 * A225656 A087913 A090585

Adjacent sequences:  A129507 A129508 A129509 * A129511 A129512 A129513

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Apr 19 2007

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 October 23 18:46 EDT 2018. Contains 316530 sequences. (Running on oeis4.)