freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-230-fibonacci-words.md

---
id: 5900f4531000cf542c50ff65
title: 'Problem 230: Fibonacci Words'
challengeType: 5
forumTopicId: 301874
dashedName: problem-230-fibonacci-words
---

# --description--

For any two strings of digits, A and B, we define FA,B to be the sequence (A,B,AB,BAB,ABBAB,...) in which each term is the concatenation of the previous two.

Further, we define DA,B(n) to be the nth digit in the first term of FA,B that contains at least n digits.

Example:

Let A=1415926535, B=8979323846. We wish to find DA,B(35), say.

The first few terms of FA,B are: 1415926535 8979323846 14159265358979323846 897932384614159265358979323846 14159265358979323846897932384614159265358979323846

Then DA,B(35) is the 35th digit in the fifth term, which is 9.

Now we use for A the first 100 digits of π behind the decimal point: 14159265358979323846264338327950288419716939937510 58209749445923078164062862089986280348253421170679

and for B the next hundred digits:

82148086513282306647093844609550582231725359408128 48111745028410270193852110555964462294895493038196 .

Find ∑n = 0,1,...,17 10n× DA,B((127+19n)×7n) .

# --hints--

`euler230()` should return 850481152593119200.

```js
assert.strictEqual(euler230(), 850481152593119200);
```

# --seed--

## --seed-contents--

```js
function euler230() {

  return true;
}

euler230();
```

# --solutions--

```js
// solution required
```