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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/harshad-or-niven-series.md

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+---
+title: Harshad or Niven series
+id: 595668ca4cfe1af2fb9818d4
+challengeType: 5
+forumTopicId: 302281
+---
+
+## Description
+<section id='description'>
+The Harshad or Niven numbers are positive integers ≥ 1 that are divisible by the sum of their digits.
+For example, <code>42</code> is a <a href="https://rosettacode.org/wiki/Harshad_or_Niven_series" title="Harshad or Niven series" target="_blank">Harshad number</a> as <code>42</code> is divisible by <code>(4 + 2)</code> without remainder.
+Assume that the series is defined as the numbers in increasing order.
+</section>
+
+## Instructions
+<section id='instructions'>
+Implement a function to generate successive members of the Harshad sequence.
+Use it to list the first twenty members of the sequence and list the first Harshad number greater than 1000.
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>isHarshadOrNiven</code> should be a function.
+    testString: assert(typeof isHarshadOrNiven === 'function');
+  - text: '<code>isHarshadOrNiven()</code> should return <code>{"firstTwenty": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],"firstOver1000": 1002}</code>'
+    testString: assert.deepEqual(isHarshadOrNiven(), res);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function isHarshadOrNiven() {
+  const res = {
+    firstTwenty: [],
+    firstOver1000: undefined
+  };
+  // Only change code below this line
+
+  return res;
+}
+```
+
+</div>
+
+
+### After Test
+<div id='js-teardown'>
+
+```js
+const res = {
+  firstTwenty: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],
+  firstOver1000: 1002
+};
+```
+
+</div>
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function isHarshadOrNiven() {
+  const res = {
+    firstTwenty: [],
+    firstOver1000: undefined
+  };
+
+  function isHarshad(n) {
+    let s = 0;
+    const nStr = n.toString();
+    for (let i = 0; i < nStr.length; ++i) {
+      s += parseInt(nStr.charAt(i), 10);
+    }
+    return n % s === 0;
+  }
+
+  let count = 0;
+  const harshads = [];
+
+  for (let n = 1; count < 20; ++n) {
+    if (isHarshad(n)) {
+      count++;
+      harshads.push(n);
+    }
+  }
+
+  res.firstTwenty = harshads;
+
+  let h = 1000;
+  while (!isHarshad(++h));
+  res.firstOver1000 = h;
+
+  return res;
+}
+
+```
+
+</section>