OFFSET
1,1
FORMULA
Like A020487 but using anti-divisors.
4, 9, 36, 576, 1296, etc. are antiharmonic both with divisors and anti-divisors.
EXAMPLE
Anti-divisors of 1212 are 5, 8, 24, 25, 97, 485, 808 and their sum is 1452. The sum of the squares of anti-divisors is 898788 and 898788/1452=619.
MAPLE
with(numtheory);
P:=proc(n)
local a, b, i, k;
for i from 3 to n do
a:=0; b:=0;
for k from 2 to i-1 do
if abs((i mod k)- k/2) < 1 then a:=a+k; b:=b+k^2; fi;
od;
if trunc(b/a)=b/a then print(i); fi;
od;
end:
P(200000);
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Jul 28 2011
EXTENSIONS
a(22)-a(37) from Donovan Johnson, Sep 22 2011
STATUS
approved