Mersenne primes: Difference between revisions
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Fixed placement
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2 ^ 19 - 1
2 ^ 31 - 1
</pre>
=={{header|ALGOL 60}}==
<works with|A60>
<syntaxhighlight lang="ALGOL">
begin
integer procedure mersenne(n);
value n; integer n;
begin
integer i, m;
m := 1;
for i := 1 step 1 until n do
m := m * 2;
mersenne := m - 1;
end;
boolean procedure isprime(n);
value n; integer n;
begin
if n < 2 then
isprime := false
else if entier(n / 2) * 2 = n then
isprime := (n = 2)
else
begin
comment - check odd divisors up to sqrt(n);
integer i, limit;
boolean divisible;
i := 3;
limit := entier(sqrt(n));
divisible := false;
for i := i while i <= limit and not divisible do
begin
if entier(n / i) * i = n then
divisible := true;
i := i + 2
end;
isprime := if divisible then false else true;
end;
end;
comment - main code begins here;
integer i, m;
outstring(1,"Searching to M(31) for Mersenne primes\n");
for i := 1 step 1 until 31 do
begin
m := mersenne(i);
if isprime(m) then
begin
outstring(1,"M(");
outinteger(1,i);
outstring(1,") : ");
outinteger(1,m);
outstring(1,"\n");
end;
end;
end
</syntaxhighlight>
{{out}}
<pre>
Searching to M(31) for Mersenne primes
M( 2 ) : 3
M( 3 ) : 7
M( 5 ) : 31
M( 7 ) : 127
M( 13 ) : 8191
M( 17 ) : 131071
M( 19 ) : 524287
M( 31 ) : 2147483647
</pre>
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</pre>
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