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A192291 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. 3
10, 14, 32, 58, 154, 182, 382, 758, 3830, 5962, 67815454, 94941602, 7172169026, 8196764584, 18624907238, 34790550682, 30033199624, 31387575416, 38857270202, 48571587730 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(21) > 10^11. - Hiroaki Yamanouchi, Sep 28 2015

LINKS

Table of n, a(n) for n=1..20.

EXAMPLE

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.

MAPLE

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);

CROSSREFS

Cf. A063990, A066272, A192290, A192292, A192293.

Sequence in context: A241162 A164765 A116955 * A144967 A328635 A260564

Adjacent sequences:  A192288 A192289 A192290 * A192292 A192293 A192294

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, Jun 29 2011

EXTENSIONS

a(11)-a(20) from Hiroaki Yamanouchi, Sep 28 2015

STATUS

approved

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Last modified March 7 19:49 EST 2021. Contains 341931 sequences. (Running on oeis4.)