Search: id:A109798
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%I A109798
%S A109798 28,40,42,52,60,96,102,104,124,110,182,182,188,210,230,234,184,358,362,
%T A109798 204,312,248,252,408,372,424,306,388,418,434,376,516,384,508,530,638,
%U A109798 782,572,888,782,828,872,592,644,820,650,938,908,1026,1034,1102,976,760
%N A109798 Second of a pair of compatible numbers, where two numbers m and n are 
               compatible if sigma(n)-2dn=sigma(m)-2dm=m+n, for some proper divisors 
               dn and dm of m and n respectively.
%H A109798 T. Trotter, <a href="http://www.trottermath.net/numthry/admirabl.html">
               Admirable Numbers.</a>
%e A109798 sigma(42)-2(1)=96-2=94 and sigma(52)-2(2)=98-4=94 and 42+52=94 so a(4)=52.
%p A109798 L:=remove(proc(z) isprime(z) end, [$1..10000]): S:=proc(n) map(proc(z) 
               sigma(n) -2*z end, divisors(n) minus {n}) end; CK:=map(proc(z) [z,
               S(z)] end, L): CL:=[]: for j from 1 to nops(CK)-1 do x:=CK[j,1]; 
               sx:=sigma(x); Sx:=CK[j,2]; for k from j+1 to nops(CK) while CK[k,
               1]<sx do y:=CK[k,1]; if x+y in Sx intersect CK[k,2] then CL:=[op(CL),
               [x,y,x+y]] fi od od;
%Y A109798 Cf. A111592.
%Y A109798 Sequence in context: A080983 A096430 A034964 this_sequence A084807 A047630 
               A135789
%Y A109798 Adjacent sequences: A109795 A109796 A109797 this_sequence A109799 A109800 
               A109801
%K A109798 nonn
%O A109798 1,1
%A A109798 Walter A. Kehowski (wkehowski(AT)cox.net), Aug 15 2005

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