TheAlgorithms · AshishKumar1297 · May 12, 2026 · May 12, 2026 · May 12, 2026 · May 12, 2026
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+package com.thealgorithms.maths;
+
+/**
+ * Neon Number algorithm.
+ * A number whose sum of digits of its square equals the number itself.
+ * Example: 9 - 9^2 = 81 - 8+1 = 9
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Recreational_mathematics">
+ *     Wikipedia</a>
+ */
+public final class NeonNumber {
+
+    private NeonNumber() {
+    }
+
+    /**
+     * Check if a number is a Neon number.
+     *
+     * @param number the input number
+     * @return true if neon number, false otherwise
+     */
+    public static boolean isNeon(final int number) {
+        int square = number * number;
+        int digitSum = 0;
+        int temp = square;
+        while (temp > 0) {
+            digitSum = digitSum + temp % 10;
+            temp /= 10;
+        }
+        return digitSum == number;
+    }
+}
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+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+public class NeonNumberTest {
+
+    @Test
+    public void testIsNeonTrue() {
+        assertTrue(NeonNumber.isNeon(0));
+        assertTrue(NeonNumber.isNeon(1));
+        assertTrue(NeonNumber.isNeon(9));
+    }
+
+    @Test
+    public void testIsNeonFalse() {
+        assertFalse(NeonNumber.isNeon(2));
+        assertFalse(NeonNumber.isNeon(5));
+        assertFalse(NeonNumber.isNeon(10));
+    }
+}