Chowla numbers: Difference between revisions
Added Algol 68
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33550336 is a perfect number
There are 5 perfect numbers < 350000000</pre>
=={{header|ALGOL 68}}==
{{Trans|C}}
<lang algol68>BEGIN # find some Chowla numbers ( Chowla n = sum of divisors of n exclusing n and 1 ) #
# returs the Chowla number of n #
PROC chowla = ( INT n )INT:
BEGIN
INT sum := 0;
FOR i FROM 2 WHILE i * i <= n DO
IF n MOD i = 0 THEN
INT j = n OVER i;
sum +:= i + IF i = j THEN 0 ELSE j FI
FI
OD;
sum
END # chowla # ;
FOR n TO 37 DO print( ( "chowla(", whole( n, 0 ), ") = ", whole( chowla( n ), 0 ), newline ) ) OD;
INT count := 0, power := 100;
FOR n FROM 2 TO 10 000 000 DO
IF chowla( n ) = 0 THEN count +:= 1 FI;
IF n MOD power = 0 THEN
print( ( "There are ", whole( count, 0 ), " primes < ", whole( power, 0 ), newline ) );
power *:= 10
FI
OD;
count := 0;
INT limit = 350 000 000;
INT k := 2, kk := 3;
WHILE INT p = k * kk;
p <= limit
DO
IF chowla( p ) = p - 1 THEN
print( ( whole( p, 0 ), " is a perfect number", newline ) );
count +:= 1
FI;
k := kk + 1; kk +:= k
OD;
print( ( "There are ", whole( count, 0 ), " perfect numbers < ", whole( limit, 0 ), newline ) )
END</lang>
{{out}}
<pre>
chowla(1) = 0
chowla(2) = 0
chowla(3) = 0
chowla(4) = 2
chowla(5) = 0
chowla(6) = 5
chowla(7) = 0
chowla(8) = 6
chowla(9) = 3
chowla(10) = 7
chowla(11) = 0
chowla(12) = 15
chowla(13) = 0
chowla(14) = 9
chowla(15) = 8
chowla(16) = 14
chowla(17) = 0
chowla(18) = 20
chowla(19) = 0
chowla(20) = 21
chowla(21) = 10
chowla(22) = 13
chowla(23) = 0
chowla(24) = 35
chowla(25) = 5
chowla(26) = 15
chowla(27) = 12
chowla(28) = 27
chowla(29) = 0
chowla(30) = 41
chowla(31) = 0
chowla(32) = 30
chowla(33) = 14
chowla(34) = 19
chowla(35) = 12
chowla(36) = 54
chowla(37) = 0
There are 25 primes < 100
There are 168 primes < 1000
There are 1229 primes < 10000
There are 9592 primes < 100000
There are 78498 primes < 1000000
There are 664579 primes < 10000000
6 is a perfect number
28 is a perfect number
496 is a perfect number
8128 is a perfect number
33550336 is a perfect number
There are 5 perfect numbers < 350000000
</pre>
=={{header|Arturo}}==
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