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A192288
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Almost anti-perfect numbers.
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2
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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, 67784277581, 79468538969, 257067141569, 290324629889, 397393221689, 445568135041, 2260763053809
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OFFSET
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1,1
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COMMENTS
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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
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LINKS
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Jud McCranie, Table of n, a(n) for n = 1..36
Eric Weisstein's World of Mathematics, Almost perfect number
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EXAMPLE
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Anti-divisors of 5881 are 2, 3, 9, 19, 619, 1307, 3921. Their sum is 5880 and 5880=5881-1.
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MAPLE
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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);
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CROSSREFS
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Cf. A066272, A073930, A192267, A192287.
Sequence in context: A304257 A217492 A178784 * A028344 A219680 A078010
Adjacent sequences: A192285 A192286 A192287 * A192289 A192290 A192291
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KEYWORD
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nonn
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AUTHOR
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Paolo P. Lava, Aug 02 2011
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EXTENSIONS
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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
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STATUS
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approved
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