# Euler problems/161 to 170

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## Revision as of 13:23, 30 January 2008

## Contents |

## 1 Problem 161

Triominoes

Solution:

problem_161 = undefined

## 2 Problem 162

Hexadecimal numbers

Solution:

problem_162 = undefined

## 3 Problem 163

Cross-hatched triangles

Solution:

problem_163 = undefined

## 4 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]]

## 5 Problem 165

Intersections

Solution:

problem_165 = undefined

## 6 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

## 7 Problem 167

Investigating Ulam sequences

Solution:

problem_167 = undefined

## 8 Problem 168

Number Rotations

Solution:

problem_168 = undefined

## 9 Problem 169

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

Solution:

fusc' 0=(1,0) fusc' n |even n=(a+b, b) |odd n=(a,a+b) where (a,b)=fusc' $div n 2 fusc =fst.fusc' problem_169=fusc (10^25)

## 10 Problem 170

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

Solution:

problem_170 = undefined