cp's OEIS Frontend

A192288 Almost anti-perfect numbers.

%I A192288 #43 Feb 16 2025 08:33:15
%S A192288 3,4,9,19,24,131,139,339,5881,14849,29501,57169,63061,65789,542781,
%T A192288 2439241,3197249,4111561,8614481,48657789,218234169,309296261,
%U A192288 731499089,1191549689,1569571661,2471800109,5687426561,9505043161,67784277581,79468538969,257067141569,290324629889,397393221689,445568135041,2260763053809
%N A192288 Almost anti-perfect numbers.
%C A192288 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.
%C A192288 a(29) > 2*10^10. - _Donovan Johnson_, Sep 22 2011
%H A192288 Jud McCranie, <a href="/A192288/b192288.txt">Table of n, a(n) for n = 1..36</a>
%H A192288 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AlmostPerfectNumber.html">Almost perfect number</a>
%e A192288 Anti-divisors of 5881 are 2, 3, 9, 19, 619, 1307, 3921. Their sum is 5880 and 5880=5881-1.
%p A192288 P:=proc(n)
%p A192288 local a,i,k;
%p A192288 for i from 3 to n do
%p A192288   a:=0;
%p A192288   for k from 2 to i-1 do
%p A192288     if abs((i mod k)-k/2)<1 then a:=a+k; fi;
%p A192288   od;
%p A192288   if i-1=a then print(i); fi;
%p A192288 od;
%p A192288 end:
%p A192288 P(1000000);
%Y A192288 Cf. A066272, A073930, A192267, A192287.
%K A192288 nonn
%O A192288 1,1
%A A192288 _Paolo P. Lava_, Aug 02 2011
%E A192288 a(15)-a(28) from _Donovan Johnson_, Sep 22 2011
%E A192288 a(29)-a(34) from _Jud McCranie_, Aug 31 2019
%E A192288 a(35) from _Jud McCranie_, Sep 05 2019