The library System.Numerics.dll, who was introduced in .Net 4.0, contains a System.Numerics.BigInteger structure. BigInteger represents a whole number of arbitrary size (or precision). Before .Net 4.0, the largest number that could be represented "out of the box" was System.Double.MaxValue. Written in decimal notation, this would be a whole number with 309 digits (more than 179 thousand centillion). However, using Double for whole number calculations is error-prone. [...]