Add A057588 Kummer Numbers sequence (TheAlgorithms#296)

OleksiiHe · web-flow · commit 03e6641fe94a · 2022-03-03T17:37:14.000+02:00
diff --git a/Algorithms.Tests/Sequences/KummerNumbersSequenceTests.cs b/Algorithms.Tests/Sequences/KummerNumbersSequenceTests.cs
@@ -0,0 +1,20 @@
+﻿using System.Linq;
+using System.Numerics;
+using Algorithms.Sequences;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Sequences
+{
+    public class KummerNumbersSequenceTests
+    {
+        [Test]
+        public void First10ElementsCorrect()
+        {
+            var sequence = new KummerNumbersSequence().Sequence.Take(10);
+            sequence.SequenceEqual(new BigInteger[] 
+                { 1, 5, 29, 209, 2309, 30029, 510509, 9699689, 223092869, 6469693229 })
+                .Should().BeTrue();
+        }
+    }
+}
diff --git a/Algorithms/Sequences/KummerNumbersSequence.cs b/Algorithms/Sequences/KummerNumbersSequence.cs
@@ -0,0 +1,37 @@
+﻿using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+
+namespace Algorithms.Sequences
+{
+    /// <summary>
+    ///     <para>
+    ///         Sequence of Kummer numbers (also called Euclid numbers of the second kind):
+    ///         -1 + product of first n consecutive primes.
+    ///     </para>
+    ///     <para>
+    ///         Wikipedia: https://wikipedia.org/wiki/Euclid_number.
+    ///     </para>
+    ///     <para>
+    ///         OEIS: https://oeis.org/A057588.
+    ///     </para>
+    /// </summary>
+    public class KummerNumbersSequence : ISequence
+    {
+        /// <summary>
+        /// Gets sequence of Kummer numbers.
+        /// </summary>
+        public IEnumerable<BigInteger> Sequence
+        {
+            get
+            {
+                var primorialNumbers = new PrimorialNumbersSequence().Sequence.Skip(1);
+
+                foreach (var n in primorialNumbers)
+                {
+                    yield return n - 1;
+                }
+            }
+        }
+    }
+}
diff --git a/README.md b/README.md
@@ -119,6 +119,7 @@ This repository contains algorithms and data structures implemented in C# for ed
     * [A007318 Binomial](./Algorithms/Sequences/BinomialSequence.cs)
     * [A010051 Binary Prime Constant](./Algorithms/Sequences/BinaryPrimeConstantSequence.cs)
     * [A011557 Powers of 10](./Algorithms/Sequences/PowersOf10Sequence.cs)
+    * [A057588 Kummer Numbers](./Algorithms/Sequences/KummerNumbersSequence.cs)
     * [A019434 Fermat Primes](./Algorithms/Sequences/FermatPrimesSequence.cs)
     * [A181391 Van Eck's](./Algorithms/Sequences/VanEcksSequence.cs)
   * [String](./Algorithms/Strings)
