43 lines
944 B
Markdown
43 lines
944 B
Markdown
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---
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id: 5900f4c71000cf542c50ffd8
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title: 'Problem 346: Strong Repunits'
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challengeType: 5
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forumTopicId: 302005
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dashedName: problem-346-strong-repunits
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---
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# --description--
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The number 7 is special, because 7 is 111 written in base 2, and 11 written in base 6 (i.e. $7_{10} = {11}_6 = {111}_2$). In other words, 7 is a repunit in at least two bases $b > 1$.
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We shall call a positive integer with this property a strong repunit. It can be verified that there are 8 strong repunits below 50: {1, 7, 13, 15, 21, 31, 40, 43}. Furthermore, the sum of all strong repunits below 1000 equals 15864.
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Find the sum of all strong repunits below ${10}^{12}$.
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# --hints--
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`strongRepunits()` should return `336108797689259260`.
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```js
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assert.strictEqual(strongRepunits(), 336108797689259260);
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```
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# --seed--
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## --seed-contents--
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```js
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function strongRepunits() {
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return true;
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}
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strongRepunits();
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```
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# --solutions--
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```js
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// solution required
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```
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