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A192288 Almost anti-perfect numbers. 1
3, 4, 9, 19, 24, 131, 139, 339, 5881, 14849, 29501, 57169, 63061, 65789, 542781, 2439241, 3197249, 4111561, 8614481, 48657789, 218234169, 309296261, 731499089, 1191549689, 1569571661, 2471800109, 5687426561, 9505043161 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..28.

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

Cf. A066272, A073930, A192267, A192287.

Sequence in context: A103295 A217492 A178784 * A028344 A219680 A078010

Adjacent sequences:  A192285 A192286 A192287 * A192289 A192290 A192291

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, Aug 02 2011

EXTENSIONS

a(15)-a(28) from Donovan Johnson, Sep 22 2011

STATUS

approved

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Last modified March 30 04:57 EDT 2017. Contains 284297 sequences.