38 lines
1.2 KiB
Text
38 lines
1.2 KiB
Text
BEGIN # find some Chowla numbers ( Chowla n = sum of divisors of n exclusing n and 1 ) #
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# returs the Chowla number of n #
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PROC chowla = ( INT n )INT:
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BEGIN
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INT sum := 0;
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FOR i FROM 2 WHILE i * i <= n DO
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IF n MOD i = 0 THEN
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INT j = n OVER i;
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sum +:= i + IF i = j THEN 0 ELSE j FI
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FI
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OD;
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sum
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END # chowla # ;
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FOR n TO 37 DO print( ( "chowla(", whole( n, 0 ), ") = ", whole( chowla( n ), 0 ), newline ) ) OD;
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INT count := 0, power := 100;
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FOR n FROM 2 TO 10 000 000 DO
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IF chowla( n ) = 0 THEN count +:= 1 FI;
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IF n MOD power = 0 THEN
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print( ( "There are ", whole( count, 0 ), " primes < ", whole( power, 0 ), newline ) );
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power *:= 10
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FI
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OD;
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count := 0;
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INT limit = 350 000 000;
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INT k := 2, kk := 3;
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WHILE INT p = k * kk;
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p <= limit
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DO
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IF chowla( p ) = p - 1 THEN
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print( ( whole( p, 0 ), " is a perfect number", newline ) );
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count +:= 1
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FI;
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k := kk + 1; kk +:= k
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OD;
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print( ( "There are ", whole( count, 0 ), " perfect numbers < ", whole( limit, 0 ), newline ) )
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END
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