Primes which contain only one odd digit: Difference between revisions
Primes which contain only one odd digit (view source)
Revision as of 17:18, 29 August 2021
, 2 years agoAdded C# entry
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Primes which contain only one even number 1-999: 78
</pre>
=={{header|C#|CSharp}}==
Modifies a conventional prime sieve to cull the items with more than one odd digit.
<lang csharp>using System;
using System.Collections.Generic;
class Program
{
// starts as an ordinary odds-only prime sieve, but becomes
// extraordinary after the else statement...
static List<uint> sieve(uint max, bool ordinary = false)
{
uint k = ((max - 3) >> 1) + 1,
lmt = ((uint)(Math.Sqrt(max++) - 3) >> 1) + 1;
var pl = new List<uint> { };
var ic = new bool[k];
for (uint i = 0, p = 3; i < lmt; i++, p += 2) if (!ic[i])
for (uint j = (p * p - 3) >> 1; j < k; j += p) ic[j] = true;
if (ordinary)
{
pl.Add(2);
for (uint i = 0, j = 3; i < k; i++, j += 2)
if (!ic[i]) pl.Add(j);
}
else
for (uint i = 0, j = 3, t = j; i < k; i++, t = j += 2)
if (!ic[i])
{
while ((t /= 10) > 0)
if (((t % 10) & 1) == 1) goto skip;
pl.Add(j);
skip:;
}
return pl;
}
static void Main(string[] args)
{
var pl = sieve((uint)1e9);
uint c = 0, l = 10, p = 1;
Console.WriteLine("List of one-odd-digit primes < 1,000:");
for (int i = 0; pl[i] < 1000; i++)
Console.Write("{0,3}{1}", pl[i], i % 9 == 8 ? "\n" : " ");
string fmt = "\nFound {0:n0} one-odd-digit primes < 10^{1} ({2:n0})";
foreach (var itm in pl)
if (itm < l) c++;
else Console.Write(fmt, c++, p++, l, l *= 10);
Console.Write(fmt, c++, p++, l);
}
}
</lang>
{{out}}
<pre>List of one-odd-digit primes < 1,000:
3 5 7 23 29 41 43 47 61
67 83 89 223 227 229 241 263 269
281 283 401 409 421 443 449 461 463
467 487 601 607 641 643 647 661 683
809 821 823 827 829 863 881 883 887
Found 3 one-odd-digit primes < 10^1 (10)
Found 12 one-odd-digit primes < 10^2 (100)
Found 45 one-odd-digit primes < 10^3 (1,000)
Found 171 one-odd-digit primes < 10^4 (10,000)
Found 619 one-odd-digit primes < 10^5 (100,000)
Found 2,560 one-odd-digit primes < 10^6 (1,000,000)
Found 10,774 one-odd-digit primes < 10^7 (10,000,000)
Found 46,708 one-odd-digit primes < 10^8 (100,000,000)
Found 202,635 one-odd-digit primes < 10^9 (1,000,000,000)</pre>
=={{header|F_Sharp|F#}}==
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