Chowla numbers: Difference between revisions
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(Chowla numbers en FreeBASIC) |
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8,128 is a number that is perfect
33,550,336 is a number that is perfect
There are 5 perfect numbers <= 35,000,000</pre>
=={{header|D}}==
{{trans|C#}}
<lang d>import std.stdio;
int chowla(int n) {
int sum;
for (int i = 2, j; i * i <= n; ++i) {
if (n % i == 0) {
sum += i + (i == (j = n / i) ? 0 : j);
}
}
return sum;
}
bool[] sieve(int limit) {
// True denotes composite, false denotes prime.
// Only interested in odd numbers >= 3
auto c = new bool[limit];
for (int i = 3; i * 3 < limit; i += 2) {
if (!c[i] && (chowla(i) == 0)) {
for (int j = 3 * i; j < limit; j += 2 * i) {
c[j] = true;
}
}
}
return c;
}
void main() {
foreach (i; 1..38) {
writefln("chowla(%d) = %d", i, chowla(i));
}
int count = 1;
int limit = cast(int)1e7;
int power = 100;
bool[] c = sieve(limit);
for (int i = 3; i < limit; i += 2) {
if (!c[i]) {
count++;
}
if (i == power - 1) {
writefln("Count of primes up to %10d = %d", power, count);
power *= 10;
}
}
count = 0;
limit = 350_000_000;
int k = 2;
int kk = 3;
int p;
for (int i = 2; ; ++i) {
p = k * kk;
if (p > limit) {
break;
}
if (chowla(p) == p - 1) {
writefln("%10d is a number that is perfect", p);
count++;
}
k = kk + 1;
kk += k;
}
writefln("There are %d perfect numbers <= 35,000,000", count);
}</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
Count of primes up to 100 = 25
Count of primes up to 1000 = 168
Count of primes up to 10000 = 1229
Count of primes up to 100000 = 9592
Count of primes up to 1000000 = 78498
Count of primes up to 10000000 = 664579
6 is a number that is perfect
28 is a number that is perfect
496 is a number that is perfect
8128 is a number that is perfect
33550336 is a number that is perfect
There are 5 perfect numbers <= 35,000,000</pre>
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