diff --git a/Bit-Manipulation/BinaryCountSetBits.js b/Bit-Manipulation/BinaryCountSetBits.js
index b879f3bd67..b959caf062 100644
--- a/Bit-Manipulation/BinaryCountSetBits.js
+++ b/Bit-Manipulation/BinaryCountSetBits.js
@@ -16,7 +16,7 @@ function BinaryCountSetBits(a) {
 
   let count = 0
   while (a) {
-    a &= (a - 1)
+    a &= a - 1
     count++
   }
 
diff --git a/DIRECTORY.md b/DIRECTORY.md
index aea7b1548f..72b8a04415 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -166,6 +166,7 @@
   * [Area](Maths/Area.js)
   * [ArithmeticGeometricMean](Maths/ArithmeticGeometricMean.js)
   * [ArmstrongNumber](Maths/ArmstrongNumber.js)
+  * [AutomorphicNumber](Maths/AutomorphicNumber.js)
   * [AverageMean](Maths/AverageMean.js)
   * [AverageMedian](Maths/AverageMedian.js)
   * [BinaryConvert](Maths/BinaryConvert.js)
@@ -280,6 +281,7 @@
   * [Problem016](Project-Euler/Problem016.js)
   * [Problem017](Project-Euler/Problem017.js)
   * [Problem018](Project-Euler/Problem018.js)
+  * [Problem019](Project-Euler/Problem019.js)
   * [Problem020](Project-Euler/Problem020.js)
   * [Problem021](Project-Euler/Problem021.js)
   * [Problem023](Project-Euler/Problem023.js)
diff --git a/Maths/AutomorphicNumber.js b/Maths/AutomorphicNumber.js
index d1b6608316..ba008271fc 100644
--- a/Maths/AutomorphicNumber.js
+++ b/Maths/AutomorphicNumber.js
@@ -35,6 +35,6 @@ export const isAutomorphic = (n) => {
     n = Math.floor(n / 10)
     n_sq = Math.floor(n_sq / 10)
   }
-  
+
   return true
 }
diff --git a/Maths/test/AutomorphicNumber.test.js b/Maths/test/AutomorphicNumber.test.js
index 19b963388c..57f40d27ee 100644
--- a/Maths/test/AutomorphicNumber.test.js
+++ b/Maths/test/AutomorphicNumber.test.js
@@ -9,19 +9,19 @@ describe('AutomorphicNumber', () => {
   })
 
   test.each([
-    { n: -3 , expected: false },
-    { n: -25 , expected: false },
+    { n: -3, expected: false },
+    { n: -25, expected: false }
   ])('should return false when n is negetive', ({ n, expected }) => {
     expect(isAutomorphic(n)).toBe(false)
   })
 
   test.each([
-    { n: 7 , expected: false },
-    { n: 83 , expected: false },
-    { n: 0 , expected: true },
-    { n: 1 , expected: true },
-    { n: 376 , expected: true },
-    { n: 90625 , expected: true },
+    { n: 7, expected: false },
+    { n: 83, expected: false },
+    { n: 0, expected: true },
+    { n: 1, expected: true },
+    { n: 376, expected: true },
+    { n: 90625, expected: true }
   ])('should return $expected when n is $n', ({ n, expected }) => {
     expect(isAutomorphic(n)).toBe(expected)
   })
diff --git a/Project-Euler/Problem006.js b/Project-Euler/Problem006.js
index 474de2ae96..804b165558 100644
--- a/Project-Euler/Problem006.js
+++ b/Project-Euler/Problem006.js
@@ -1,8 +1,8 @@
 // https://projecteuler.net/problem=6
 
 export const squareDifference = (num = 100) => {
-  let sumOfSquares = (num)*(num+1)*(2*num+1)/6
-  let sums = (num*(num+1))/2
-  
+  let sumOfSquares = (num * (num + 1) * (2 * num + 1)) / 6
+  let sums = (num * (num + 1)) / 2
+
   return sums ** 2 - sumOfSquares // difference of square of the total sum and sum of squares
 }
diff --git a/Project-Euler/Problem019.js b/Project-Euler/Problem019.js
new file mode 100644
index 0000000000..79a3ad7c43
--- /dev/null
+++ b/Project-Euler/Problem019.js
@@ -0,0 +1,19 @@
+// https://projecteuler.net/problem=19
+
+export const countSundays = (startYear = 1901, endYear = 2000) => {
+  let n = 0
+  let dayOfWeek = 2
+  const months = [31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+
+  for (let year = startYear; year <= endYear; year++) {
+    months[1] = 28 + ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0)
+
+    for (const month of months) {
+      dayOfWeek += month % 7
+      if (dayOfWeek % 7 === 0) {
+        n++
+      }
+    }
+  }
+  return n
+}
diff --git a/Project-Euler/test/Problem004.test.js b/Project-Euler/test/Problem004.test.js
new file mode 100644
index 0000000000..cd6a55ac98
--- /dev/null
+++ b/Project-Euler/test/Problem004.test.js
@@ -0,0 +1,11 @@
+import { largestPalindromic } from '../Problem004.js'
+
+describe('Largest Palindromic Number', () => {
+  test('if digit is 2', () => {
+    expect(largestPalindromic(2)).toBe(9009)
+  })
+  // Project Euler Condition Check
+  test('if digit is 3', () => {
+    expect(largestPalindromic(3)).toBe(906609)
+  })
+})
diff --git a/Project-Euler/test/Problem019.test.js b/Project-Euler/test/Problem019.test.js
new file mode 100644
index 0000000000..6e1a050e53
--- /dev/null
+++ b/Project-Euler/test/Problem019.test.js
@@ -0,0 +1,11 @@
+import { countSundays } from '../Problem019.js'
+
+describe('Count Sundays', () => {
+  test('when start year is 1801 and end year is 1900', () => {
+    expect(countSundays(1801, 1900)).toBe(172)
+  })
+  // Project Euler Condition Check
+  test('when start year is 1901 and end year is 2000', () => {
+    expect(countSundays()).toBe(171)
+  })
+})
diff --git a/Recursive/test/BinaryEquivalent.test.js b/Recursive/test/BinaryEquivalent.test.js
index b79a455eed..ddabb7d477 100644
--- a/Recursive/test/BinaryEquivalent.test.js
+++ b/Recursive/test/BinaryEquivalent.test.js
@@ -1,29 +1,29 @@
-import { binaryEquivalent } from "../BinaryEquivalent";
+import { binaryEquivalent } from '../BinaryEquivalent'
 
 const tests = [
-    {
-        test: 2,
-        expectedValue: "10"
-    },
-    {       
-        test: 0,
-        expectedValue: "0"
-    },
-    {
-        test: 543,
-        expectedValue: "1000011111"
-    },
-    {
-        test: 4697621023,
-        expectedValue: "100011000000000000000001000011111"
-    }
+  {
+    test: 2,
+    expectedValue: '10'
+  },
+  {
+    test: 0,
+    expectedValue: '0'
+  },
+  {
+    test: 543,
+    expectedValue: '1000011111'
+  },
+  {
+    test: 4697621023,
+    expectedValue: '100011000000000000000001000011111'
+  }
 ]
 
-describe("Binary Equivalent", () => {
-    test.each(tests)(
-        "of $test should be $expectedValue",
-        ({test, expectedValue}) => {
-            expect(binaryEquivalent(test)).toBe(expectedValue);
-        }
-    )
+describe('Binary Equivalent', () => {
+  test.each(tests)(
+    'of $test should be $expectedValue',
+    ({ test, expectedValue }) => {
+      expect(binaryEquivalent(test)).toBe(expectedValue)
+    }
+  )
 })
diff --git a/Search/InterpolationSearch.js b/Search/InterpolationSearch.js
index e6deae496f..93f3b78b0e 100644
--- a/Search/InterpolationSearch.js
+++ b/Search/InterpolationSearch.js
@@ -36,4 +36,4 @@ export function interpolationSearch(arr, key) {
   }
 
   return -1
-}
\ No newline at end of file
+}