2018-09-30 23:01:58 +01:00
---
id: 5900f4741000cf542c50ff86
2018-10-20 21:02:47 +03:00
title: 'Problem 263: An engineers'' dream come true'
2020-11-27 19:02:05 +01:00
challengeType: 5
2019-08-05 09:17:33 -07:00
forumTopicId: 301912
2021-01-13 03:31:00 +01:00
dashedName: problem-263-an-engineers-dream-come-true
2018-09-30 23:01:58 +01:00
---
2020-11-27 19:02:05 +01:00
# --description--
2018-09-30 23:01:58 +01:00
Consider the number 6. The divisors of 6 are: 1,2,3 and 6.
2020-11-27 19:02:05 +01:00
2018-09-30 23:01:58 +01:00
Every number from 1 up to and including 6 can be written as a sum of distinct divisors of 6:
2020-11-27 19:02:05 +01:00
2021-07-24 09:09:54 +02:00
$1 = 1$, $2 = 2$, $3 = 1 + 2$, $4 = 1 + 3$, $5 = 2 + 3$, $6 = 6$.
2018-09-30 23:01:58 +01:00
2021-07-24 09:09:54 +02:00
A number $n$ is called a practical number if every number from 1 up to and including $n$ can be expressed as a sum of distinct divisors of $n$.
2018-09-30 23:01:58 +01:00
A pair of consecutive prime numbers with a difference of six is called a sexy pair (since "sex" is the Latin word for "six"). The first sexy pair is (23, 29).
We may occasionally find a triple-pair, which means three consecutive sexy prime pairs, such that the second member of each pair is the first member of the next pair.
2021-07-24 09:09:54 +02:00
We shall call a number $n$ such that:
- ($n - 9$, $n - 3$), ($n - 3$, $n + 3$), ($n + 3$, $n + 9$) form a triple-pair, and
- the numbers $n - 8$, $n - 4$, $n$, $n + 4$ and $n + 8$ are all practical,
2018-09-30 23:01:58 +01:00
an engineers’ paradise.
Find the sum of the first four engineers’ paradises.
2020-11-27 19:02:05 +01:00
# --hints--
2018-09-30 23:01:58 +01:00
2021-07-24 09:09:54 +02:00
`engineersDreamComeTrue()` should return `2039506520` .
2018-09-30 23:01:58 +01:00
2020-11-27 19:02:05 +01:00
```js
2021-07-24 09:09:54 +02:00
assert.strictEqual(engineersDreamComeTrue(), 2039506520);
2018-09-30 23:01:58 +01:00
```
2020-11-27 19:02:05 +01:00
# --seed--
2018-09-30 23:01:58 +01:00
2020-11-27 19:02:05 +01:00
## --seed-contents--
2018-09-30 23:01:58 +01:00
```js
2021-07-24 09:09:54 +02:00
function engineersDreamComeTrue() {
2020-09-15 09:57:40 -07:00
2018-09-30 23:01:58 +01:00
return true;
}
2021-07-24 09:09:54 +02:00
engineersDreamComeTrue();
2018-09-30 23:01:58 +01:00
```
2020-11-27 19:02:05 +01:00
# --solutions--
2018-09-30 23:01:58 +01:00
```js
// solution required
```