**ID** | Description / Title | **Solved By** |

151 | Paper sheets of standard sizes: an expected-value problem | 2963 |

152 | Writing 1/2 as a sum of inverse squares | 1423 |

153 | Investigating Gaussian Integers | 1388 |

154 | Exploring Pascal's pyramid | 1456 |

155 | Counting Capacitor Circuits | 1921 |

156 | Counting Digits | 1301 |

157 | Solving the diophantine equation ^{1}/_{a}+^{1}/_{b}= ^{p}/_{10n} | 1465 |

158 | Exploring strings for which only one character comes lexicographically after its neighbour to the left | 2051 |

159 | Digital root sums of factorisations | 1851 |

160 | Factorial trailing digits | 1824 |

161 | Triominoes | 1150 |

162 | Hexadecimal numbers | 3174 |

163 | Cross-hatched triangles | 1048 |

164 | Numbers for which no three consecutive digits have a sum greater than a given value | 3347 |

165 | Intersections | 1440 |

166 | Criss Cross | 2291 |

167 | Investigating Ulam sequences | 970 |

168 | Number Rotations | 1520 |

169 | Exploring the number of different ways a number can be expressed as a sum of powers of 2 | 2734 |

170 | Find the largest 0 to 9 pandigital that can be formed by concatenating products | 1107 |

171 | Finding numbers for which the sum of the squares of the digits is a square | 1508 |

172 | Investigating numbers with few repeated digits | 2170 |

173 | Using up to one million tiles how many different "hollow" square laminae can be formed? | 5350 |

174 | Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements | 3525 |

175 | Fractions involving the number of different ways a number can be expressed as a sum of powers of 2 | 1060 |

176 | Right-angled triangles that share a cathetus | 1121 |

177 | Integer angled Quadrilaterals | 747 |

178 | Step Numbers | 1980 |

179 | Consecutive positive divisors | 6650 |

180 | Rational zeros of a function of three variables | 897 |

181 | Investigating in how many ways objects of two different colours can be grouped | 1120 |

182 | RSA encryption | 1485 |

183 | Maximum product of parts | 2879 |

184 | Triangles containing the origin | 941 |

185 | Number Mind | 1804 |

186 | Connectedness of a network | 1648 |

187 | Semiprimes | 6520 |

188 | The hyperexponentiation of a number | 3904 |

189 | Tri-colouring a triangular grid | 1150 |

190 | Maximising a weighted product | 2445 |

191 | Prize Strings | 4191 |

192 | Best Approximations | 906 |

193 | Squarefree Numbers | 1807 |

194 | Coloured Configurations | 808 |

195 | Inscribed circles of triangles with one angle of 60 degrees | 763 |

196 | Prime triplets | 1406 |

197 | Investigating the behaviour of a recursively defined sequence | 3102 |

198 | Ambiguous Numbers | 641 |

199 | Iterative Circle Packing | 1060 |

200 | Find the 200th prime-proof sqube containing the contiguous sub-string "200" | 1311 |