OFFSET
1,1
COMMENTS
An almost anti-perfect number is a least anti-deficient number, i.e., one such that sigma*(n)=n-1, where sigma*(n) is the sum of the anti-divisors of n. Like almost perfect numbers (see link) but using anti-divisors.
a(29) > 2*10^10. - Donovan Johnson, Sep 22 2011
LINKS
Jud McCranie, Table of n, a(n) for n = 1..36
Eric Weisstein's World of Mathematics, Almost perfect number
EXAMPLE
Anti-divisors of 5881 are 2, 3, 9, 19, 619, 1307, 3921. Their sum is 5880 and 5880=5881-1.
MAPLE
P:=proc(n)
local a, i, k;
for i from 3 to n do
a:=0;
for k from 2 to i-1 do
if abs((i mod k)-k/2)<1 then a:=a+k; fi;
od;
if i-1=a then print(i); fi;
od;
end:
P(1000000);
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Aug 02 2011
EXTENSIONS
a(15)-a(28) from Donovan Johnson, Sep 22 2011
a(29)-a(34) from Jud McCranie, Aug 31 2019
a(35) from Jud McCranie, Sep 05 2019
STATUS
approved