OFFSET
1,4
COMMENTS
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 19 2007
STATUS
approved