Decimal to HexaDecimal Data conversion

// add a reference to System.Numerics.dll, then add this line at the top of your code file:
using System.Numerics;

// decimal to hex:
BigInteger dec = BigInteger.Parse("1011406131533376933715533");
string hex = dec.ToString("X");
Console.WriteLine(hex); // output: 0D62C6FAE52427AB5DE4D

// hex to decimal:
string hex2 = "0D62C6FAE52427AB5DE4D";
BigInteger dec2 = BigInteger.Parse(hex2, System.Globalization.NumberStyles.HexNumber);
Console.WriteLine(dec2); // output: 1011406131533376933715533