---
id: 5900f4831000cf542c50ff95
title: 'Problem 278: Linear Combinations of Semiprimes'
challengeType: 5
forumTopicId: 301928
dashedName: problem-278-linear-combinations-of-semiprimes
---

# --description--

Given the values of integers 1 < a1 < a2 <... < an, consider the linear combination q1a1 + q2a2 + ... + qnan = b, using only integer values qk ≥ 0.

Note that for a given set of ak, it may be that not all values of b are possible. For instance, if a1 = 5 and a2 = 7, there are no q1 ≥ 0 and q2 ≥ 0 such that b could be 1, 2, 3, 4, 6, 8, 9, 11, 13, 16, 18 or 23.

In fact, 23 is the largest impossible value of b for a1 = 5 and a2 = 7. We therefore call f(5, 7) = 23. Similarly, it can be shown that f(6, 10, 15)=29 and f(14, 22, 77) = 195.

Find ∑ f(p*q,p*r,q\*r), where p, q and r are prime numbers and p < q < r < 5000.

# --hints--

`euler278()` should return 1228215747273908500.

```js
assert.strictEqual(euler278(), 1228215747273908500);
```

# --seed--

## --seed-contents--

```js
function euler278() {

  return true;
}

euler278();
```

# --solutions--

```js
// solution required
```