Solved 42 and 43.

ipython/EulerProblem044.ipynb

@@ -0,0 +1,60 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Pentagon numbers (Euler Problem 44)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": true
+   },
+   "source": [
+    "[https://projecteuler.net/problem=44](https://projecteuler.net/problem=44)\n",
+    "\n",
+    "Pentagonal numbers are generated by the formula, $P_n=n(3n−1)/2$. The first ten pentagonal numbers are:\n",
+    "\n",
+    "    1, 5, 12, 22, 35, 51, 70, 92, 117, 145, ...\n",
+    "\n",
+    "It can be seen that $P_4 + P_7 = 22 + 70 = 92 = P_8$. However, their difference, 70 − 22 = 48, is not pentagonal.\n",
+    "\n",
+    "Find the pair of pentagonal numbers, $P_j$ and $P_k$, for which their sum and difference are pentagonal and $D = |P_k − P_j|$ is minimised; what is the value of D?"
+   ]
+  },
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