Add NeonNumber algorithm in maths package

src/main/java/com/thealgorithms/maths/NeonNumber.java

@@ -0,0 +1,39 @@
+package com.thealgorithms.maths;
+
+/**
+ * This class checks whether a number is a Neon Number.
+ * A Neon number is a number where the sum of digits of
+ * its square is equal to the number itself.
+ *
+ * Example:
+ * 9^2 = 81 → 8 + 1 = 9 (Neon Number)
+ */
+public final class NeonNumber {
+
+    private NeonNumber() {
+        // Prevent instantiation
+    }
+
+    /**
+     * Checks if a number is a Neon Number.
+     *
+     * @param number the input number
+     * @return true if the number is a Neon Number, otherwise false
+     * @throws IllegalArgumentException if the number is negative
+     */
+    public static boolean isNeon(int number) {
+        if (number < 0) {
+            throw new IllegalArgumentException("Number must be non-negative");
+        }
+
+        int square = number * number;
+        int sum = 0;
+
+        while (square > 0) {
+            sum += square % 10;
+            square /= 10;
+        }
+
+        return sum == number;
+    }
+}