The BigInteger type is an immutable type that represents an arbitrarily large integer; in theory, it has no upper or lower bounds.
Like Burkhard and Hank , you should use BigInteger.Parse() for this.
BigInteger number= BigInteger.Parse("27419669081321110693270343633073797");
Also do not forget;
If you use the Parse() method to round the string representation of a BigInteger that was output by the ToString method, you must use the BigInteger.ToString(String) method with the format “R” specifier to create the string representation of the BigInteger value. Otherwise, the BigInteger string representation only stores the 50 most significant digits of the original value, and data may be lost when using the Parse method to restore the BigInteger value.
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