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curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-16-power-digit-sum.md

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+---
+id: 5900f37d1000cf542c50fe8f
+challengeType: 5
+title: 'Problem 16: Power digit sum'
+forumTopicId: 301791
+---
+
+## Description
+<section id='description'>
+
+2<sup>15</sup> = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.
+
+What is the sum of the digits of the number 2<sup>`exponent`</sup>?
+
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>powerDigitSum(15)</code> should return a number.
+    testString: assert(typeof powerDigitSum(15) === 'number');
+  - text: <code>powerDigitSum(15)</code> should return 26.
+    testString: assert.strictEqual(powerDigitSum(15), 26);
+  - text: <code>powerDigitSum(128)</code> should return 166.
+    testString: assert.strictEqual(powerDigitSum(128), 166);
+  - text: <code>powerDigitSum(1000)</code> should return 1366.
+    testString: assert.strictEqual(powerDigitSum(1000), 1366);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function powerDigitSum(exponent) {
+
+  return true;
+}
+
+powerDigitSum(15);
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function powerDigitSum(exponent) {
+  const bigNum = [1];
+  let sum = 0;
+
+  for (let i = 1; i <= exponent; i++) {
+    let count = bigNum.length + 1;
+    let overflow = 0;
+    for (let j = 0; j < count; j++) {
+      let digit = bigNum[j] || 0;
+      digit = 2 * digit + overflow;
+
+      if (digit > 9) {
+        digit -= 10;
+        overflow = 1;
+      } else {
+        overflow = 0;
+      }
+
+      bigNum[j] = digit;
+    }
+  }
+
+  bigNum.forEach(function(num) {
+    return sum += num;
+  });
+
+  return sum;
+}
+```
+
+</section>