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    <p>To see how to find the factors of a given number in C# see <a href="https://stackoverflow.com/questions/239865/best-way-to-find-all-factors-of-a-given-number-in-c">this (duplicate?) StackOverflow question</a>.</p> <p>A few points on your code:</p> <ul> <li>there is no need for recursion if using a naive search, just build a list of factors within the method and return it at the end (or use <code>yield</code>).</li> <li>your second if statement is redundant as it wraps a while loop with the same condition.</li> <li>you should use an integer type (and unsigned integer types will allow larger numbers than their signed counterparts, e.g. <code>uint</code> or <code>ulong</code>) rather than <code>decimal</code> as you are working with integers. For arbitrarily large integers, use <code>System.Numerics.BigInteger</code>.</li> <li>if you search incrementally upwards for a factor, you can stop looking when you have got as far as the square root of the original number, as no factor can be larger than that.</li> </ul> <p>Also, note that there is no known efficient algorithm for factoring large numbers (see <a href="http://en.wikipedia.org/wiki/Integer_factorization" rel="nofollow noreferrer">Wikipedia</a> for a brief overview).</p> <p>Here's example code, based on the above observations:</p> <pre><code>static IList&lt;BigInteger&gt; GetFactors(BigInteger n) { List&lt;BigInteger&gt; factors = new List&lt;BigInteger&gt;(); BigInteger x = 2; while (x &lt;= n) { if (n % x == 0) { factors.Add(x); n = n / x; } else { x++; if (x * x &gt;= n) { factors.Add(n); break; } } } return factors; } </code></pre> <p>Note that this is still a rather naive algorithm which could easily be further improved.</p>
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    1. POFactorizing largest number
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    1. COyes i agree with your 2nd point regarding redundant if statement .. I will do correction in my code ... If I use int as data type then it will not support this big number 18991325453139 .. that's why I have used decimal as data type ...
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    2. COIf you want to factorize number that high, you should use the integer type `ulong` (aka `UInt64`). For arbitrarily large integers, you can use `System.Numerics.BigInteger`. I've updated my answer to include sample code.
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