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**Vampire Number in C# with Examples**

In this article, I am going to discuss **Vampire** **Number Program in C#** with Examples. Please read our previous article where we discussed the **Krishnamurthy** **Number Program in C#**. Here, in this article, first, we will learn what is a Vampire Number and then we will see how to implement Vampire Number Program in C#.

**What is a Vampire Number?**

A vampire number is a natural number with an even number of digits, that can be factored into two integers. For example, 1260 is a vampire number, with 21 and 60 as fangs, since 21 × 60 = 1260.

126000 (which can be expressed as 21 × 6000 or 210 × 600) is not, as 21 and 6000 do not have the correct length, and both 210 and 600 have trailing zeroes

Some of the vampire numbers are:

1260, 1395, 1435, 1530, 1827, 2187, 6880, 102510, 104260, 105210, 105264, 105750, 108135, 110758, 115672, 116725, 117067, 118440, 120600, 123354, 124483, 125248, 125433, 125460, 125500, …

**Multiple fang pairs **

A vampire number can have multiple distinct pairs of fangs.

The first of infinitely many vampire numbers with 2 pairs of fangs: **125460 = 204 × 615 = 246 × 510**

The first with 3 pairs of fangs: **13078260 = 1620 × 8073 = 1863 × 7020 = 2070 × 6318**

The first with 4 pairs of fangs: **16758243290880 = 1982736 × 8452080 = 2123856 × 7890480 = 2751840 × 6089832 = 2817360 × 5948208**

**How to implement Vampire Number Program in C#?**

In mathematics, a vampire number (or true vampire number) is a composite natural number v, with an even number of digits n, that can be factored into two integers x and y each with n/2 digits and not both with trailing zeroes, where v contains precisely all the digits from x and from y, in any order, counting multiplicity. x and y are called the fangs.

Condition for a number to be Vampire Number:

- Has a pair number of digits. Let’s call the number of digits: n
- You can obtain the number by multiplying two integers, x, and y, each with n/2 digits. x and y are the fangs.
- Both fangs cannot end simultaneously in 0.
- The number can be made with all digits from x and y, in any order and only using each digit once.

**Example:**

Positive natural number v = 1260

Even number of digits n = 4

Two integers x = 21 and y = 60 (Each integer contains n/2 i.e. 4/2 = 2 digits). There are no trailing zeros. Here, x and y are called fangs. Multiply x and y will give you 1260 and hence it is a Vampire Number

**Example: Vampire Number Program in C#**

The following sample code shows how to implement the Vampire number program in C#.

using System; namespace VampireNumber { class Program { static void Main(string[] args) { int i, j, n; ulong x; var f = new ulong[16]; var bigs = new ulong[] { 16758243290880UL, 24959017348650UL, 14593825548650UL, 0 }; ulong[] tens = new ulong[20]; tens[0] = 1; for (i = 1; i < 20; i++) tens[i] = tens[i - 1] * 10; for (x = 1, n = 0; n < 25; x++) { if ((j = fangs(x, f, tens)) == 0) continue; Console.Write(++n + ": "); show_fangs(x, f, j); } Console.WriteLine(); for (i = 0; bigs[i] > 0; i++) { if ((j = fangs(bigs[i], f, tens)) > 0) show_fangs(bigs[i], f, j); else Console.WriteLine(bigs[i] + " is not vampiric."); } Console.ReadLine(); } private static void show_fangs(ulong x, ulong[] f, int cnt) { Console.Write(x); int i; for (i = 0; i < cnt; i++) Console.Write(" = " + f[i] + " * " + (x / f[i])); Console.WriteLine(); } private static int fangs(ulong x, ulong[] f, ulong[] tens) { int n = 0; int nd = ndigits(x); if ((nd & 1) > 0) return 0; nd /= 2; ulong lo, hi; lo = Math.Max(tens[nd - 1], (x + tens[nd] - 2) / (tens[nd] - 1)); hi = Math.Min(x / lo, (ulong)Math.Sqrt(x)); ulong a, b, t = dtally(x); for (a = lo; a <= hi; a++) { b = x / a; if (a * b == x && ((a % 10) > 0 || (b % 10) > 0) && t == dtally(a) + dtally(b)) f[n++] = a; } return n; } private static ulong dtally(ulong x) { ulong t = 0; while (x > 0) { t += 1UL << (int)((x % 10) * 6); x /= 10; } return t; } private static int ndigits(ulong x) { int n = 0; while (x > 0) { n++; x /= 10; } return n; } } }

**Output:**

In the next article, I am going to discuss the **Happy Number Program in C#** with Examples. Here, in this article, I try to explain **How to Implement Vampire** **Number Program in C#** with Examples and I hope you enjoy this Vampire Number Program in the C# article.

**About the Author: Pranaya Rout**

Pranaya Rout has published more than 3,000 articles in his 11-year career. Pranaya Rout has very good experience with Microsoft Technologies, Including C#, VB, ASP.NET MVC, ASP.NET Web API, EF, EF Core, ADO.NET, LINQ, SQL Server, MYSQL, Oracle, ASP.NET Core, Cloud Computing, Microservices, Design Patterns and still learning new technologies.