43 lines
1.3 KiB
Markdown
43 lines
1.3 KiB
Markdown
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---
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id: 5900f3ec1000cf542c50feff
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title: 'Problem 128: Hexagonal tile differences'
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challengeType: 5
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forumTopicId: 301755
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dashedName: problem-128-hexagonal-tile-differences
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---
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# --description--
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A hexagonal tile with number 1 is surrounded by a ring of six hexagonal tiles, starting at "12 o'clock" and numbering the tiles 2 to 7 in an anti-clockwise direction.
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New rings are added in the same fashion, with the next rings being numbered 8 to 19, 20 to 37, 38 to 61, and so on. The diagram below shows the first three rings.
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By finding the difference between tile n and each of its six neighbours we shall define PD(n) to be the number of those differences which are prime. For example, working clockwise around tile 8 the differences are 12, 29, 11, 6, 1, and 13. So PD(8) = 3. In the same way, the differences around tile 17 are 1, 17, 16, 1, 11, and 10, hence PD(17) = 2. It can be shown that the maximum value of PD(n) is 3. If all of the tiles for which PD(n) = 3 are listed in ascending order to form a sequence, the 10th tile would be 271. Find the 2000th tile in this sequence.
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# --hints--
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`euler128()` should return 14516824220.
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```js
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assert.strictEqual(euler128(), 14516824220);
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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 euler128() {
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return true;
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}
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euler128();
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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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