Amicable pairs: Difference between revisions
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17296 18416 found after 2.240 seconds
2.250 seconds total search time</pre>
==={{header|PL/I-80}}===
Rather than populating an array with the sums of the proper divisors preparatory to a search, the approach here performs an immediate direct test, saving memory, and at no observable penalty in execution speed, even though about 25% more calls are made to sumf() than would be required simply to initialize the array.
<lang PL/I>
amicable: procedure options (main);
%replace
search_limit by 20000;
dcl (a, b, found) fixed bin;
put skip list ('Searching for amicable pairs up to ');
put edit (search_limit) (f(5));
found = 0;
do a = 2 to search_limit;
b = sumf(a);
if (b > a) then
do;
if (sumf(b) = a) then
do;
found = found + 1;
put skip edit (a,b) (f(7));
end;
end;
end;
put skip list (found, ' pairs were found');
stop;
/* return sum of the proper divisors of n */
sumf: procedure(n) returns (fixed bin);
dcl (n, sum, f1, f2) fixed bin;
sum = 1; /* 1 is a proper divisor of every number */
f1 = 2;
do while ((f1 * f1) < n);
if mod(n, f1) = 0 then
do;
sum = sum + f1;
f2 = n / f1;
/* don't double count identical co-factors! */
if f2 > f1 then sum = sum + f2;
end;
f1 = f1 + 1;
end;
return (sum);
end sumf;
end amicable;
</lang>
{{out}}
<pre>
Searching for amicable pairs up to 20000
220 284
1184 1210
2620 2924
5020 5564
6232 6368
10744 10856
12285 14595
17296 18416
8 pairs were found
</pre>
=={{header|PL/M}}==
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