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A192291
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Couple of numbers a, b for which sigma*(a)=b and sigma(b)-b=a, where sigma*(n) is the sum of the anti-divisors of n.
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3
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10, 14, 32, 58, 154, 182, 382, 758, 3830, 5962, 67815454, 94941602, 7172169026, 8196764584, 18624907238, 34790550682, 30033199624, 31387575416, 38857270202, 48571587730
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OFFSET
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1,1
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COMMENTS
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a(21) > 10^11. - Hiroaki Yamanouchi, Sep 28 2015
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LINKS
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Table of n, a(n) for n=1..20.
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EXAMPLE
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sigma*(10) = 3+4+7 = 14.
sigma(14)-14 = 1+2+7 = 10.
sigma*(32)= 3+5+7+9+13+21 = 58.
sigma(58)-58 = 1+2+29 = 32.
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MAPLE
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with(numtheory);
P:= proc(n)
local a, b, c, i, ks;
for i from 3 to n do
a:={};
for k from 2 to i-1 do
if abs((i mod k)- k/2) < 1 then
a:=a union {k};
fi;
od;
b:=nops(a); c:=op(a); s:=0;
for k from 1 to b do
s:=s+c[k];
od;
if sigma(s)-s=i then
print(i, s);
fi;
od;
end:
P(10000);
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CROSSREFS
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Cf. A063990, A066272, A192290, A192292, A192293.
Sequence in context: A241162 A164765 A116955 * A144967 A328635 A260564
Adjacent sequences: A192288 A192289 A192290 * A192292 A192293 A192294
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KEYWORD
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nonn,more
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AUTHOR
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Paolo P. Lava, Jun 29 2011
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EXTENSIONS
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a(11)-a(20) from Hiroaki Yamanouchi, Sep 28 2015
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STATUS
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approved
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