Add Sequence A000292 (TheAlgorithms#355)

Author: RichardVasquez

Algorithms.Tests/Sequences/TetrahedralSequenceTests.cs

@@ -0,0 +1,30 @@
+using System.Linq;
+using System.Numerics;
+using Algorithms.Sequences;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Sequences;
+
+[TestFixture]
+public class TetrahedralSequenceTests
+{
+    private static readonly BigInteger[] TestList = {
+                                                        0, 1, 4, 10, 20, 35, 56, 84, 120, 165, 220, 286, 364, 455,
+                                                        560, 680, 816, 969, 1140, 1330, 1540, 1771, 2024, 2300,
+                                                        2600, 2925, 3276, 3654, 4060, 4495, 4960, 5456, 5984, 6545,
+                                                        7140, 7770, 8436, 9139, 9880, 10660, 11480, 12341, 13244,
+                                                        14190, 15180,
+                                                    };
+
+    /// <summary>
+    ///     This test uses the list values provided from http://oeis.org/A000292/list.
+    /// </summary>
+    [Test]
+    public void TestOeisList()
+    {
+        var sequence = new TetrahedralSequence().Sequence.Take(TestList.Length);
+        sequence.SequenceEqual(TestList).Should().BeTrue();
+
+    }
+}

Algorithms/Sequences/TetrahedralSequence.cs

@@ -0,0 +1,42 @@
+using System.Collections.Generic;
+using System.Numerics;
+
+namespace Algorithms.Sequences;
+
+/// <summary>
+///     <para>
+///         Sequence of tetrahedral (triangular pyramids) counts for n >= 0.
+///     </para>
+///     <para>
+///         OEIS: http://oeis.org/A000292.
+///     </para>
+///     <para>
+///         Wikipedia: https://en.wikipedia.org/wiki/Tetrahedral_number.
+///     </para>
+/// </summary>
+public class TetrahedralSequence : ISequence
+{
+    /// <summary>
+    ///     <para>
+    ///         Gets the value of packing spheres in a regular tetrahedron
+    ///         with increasing by 1 triangular numbers under each layer.
+    ///     </para>
+    ///     <para>
+    ///         It can be reviewed by starting at the 4th row of Pascal's Triangle
+    ///         following the diagonal values going into the triangle.
+    ///     </para>
+    /// </summary>
+    public IEnumerable<BigInteger> Sequence
+    {
+        get
+        {
+            var index = BigInteger.Zero;
+            var six = new BigInteger(6);
+            while (true)
+            {
+                yield return BigInteger.Divide(index * (index + 1) * (index + 2), six);
+                index++;
+            }
+        }
+    }
+}

README.md

@@ -138,6 +138,7 @@ find more than one implementation for the same objective but using different alg
     * [A000142 Factorial](./Algorithms/Sequences/FactorialSequence.cs)
     * [A000215 Fermat Numbers](./Algorithms/Sequences/FermatNumbersSequence.cs)
     * [A000290 Squares](./Algorithms/Sequences/SquaresSequence.cs)
+    * [A000292 Tetrahedral numbers](./Algorithms/Sequences/TetrahedralSequence.cs)
     * [A000578 Cubes](./Algorithms/Sequences/CubesSequence.cs)
     * [A000720 PrimePi](./Algorithms/Sequences/PrimePiSequence.cs)
     * [A001146 Number of Boolean Functions](./Algorithms/Sequences/NumberOfBooleanFunctionsSequence.cs)