# Euler problems/171 to 180

From HaskellWiki

## Contents

## Problem 161

Triominoes

Solution:

```
problem_161 = undefined
```

## Problem 162

Hexadecimal numbers

Solution:

```
problem_162 = undefined
```

## Problem 163

Cross-hatched triangles

Solution:

```
problem_163 = undefined
```

## Problem 164

Numbers for which no three consecutive digits have a sum greater than a given value.

Solution:

```
addDigit x = [[sum [x !! b !! c | c <- [0..9-a-b]] | b <- [0..9-a]] | a<-[0..9]]
x3 = [[10-a-b | b <- [0..9-a]] | a <- [0..9]]
x20 = iterate addDigit x3 !! 17
problem_164 = sum [x20 !! a !! b | a <- [1..9], b <- [0..9-a]]
```

## Problem 165

Intersections

Solution:

```
problem_165 = undefined
```

## Problem 166

Criss Cross

Solution:

```
problem_166 =
sum [ product (map count [[0, c, b-d, a-b-d],
[0, b-a, c+d-a, b+d-a],
[0, -b-c, a-b-c-d, -c-d],
[0, a, d, c+d]])|
a <- [-9..9],
b <- [-9+a..9+a],
c <- [-9..9],
d <- [-9+a-c..9+a-c]]
where
count xs
|u<l=0
|otherwise=u-l+1
where
l = -minimum xs
u = 9-maximum xs
```

## Problem 167

Investigating Ulam sequences

Solution:

```
problem_167 = undefined
```

## Problem 168

Number Rotations

Solution:

```
problem_168 = undefined
```

## Problem 169

Exploring the number of different ways a number can be expressed as a sum of powers of 2.

Solution:

```
problem_169 = undefined
```

## Problem 170

Find the largest 0 to 9 pandigital that can be formed by concatenating products.

Solution:

```
problem_170 = undefined
```