diff --git a/notebooks/problem0046.ipynb b/notebooks/problem0046.ipynb new file mode 100644 index 0000000..0c5ea5c --- /dev/null +++ b/notebooks/problem0046.ipynb @@ -0,0 +1,93 @@ +{ + "cells": [ + { + "cell_type": "markdown", + "id": "42fd0b2c", + "metadata": {}, + "source": [ + "# [Goldbach's Other Conjecture](https://projecteuler.net/problem=46)\n", + "\n", + "We can write a function that takes odd composites $m$ and checks successively larger values of $n$ to see if $m - 2n^2$ is prime. If we find such an $n$, $m$ satisfies the conjecture, but if $n$ gets too large, $m - 2n^2$ will become non-positive, and therefore can't be prime, so $m$ fails to satisfy the conjecture." + ] + }, + { + "cell_type": "code", + "execution_count": 1, + "id": "eba09d52", + "metadata": {}, + "outputs": [ + { + "data": { + "text/plain": [ + "5777" + ] + }, + "execution_count": 1, + "metadata": {}, + "output_type": "execute_result" + } + ], + "source": [ + "from itertools import count\n", + "\n", + "def satisfies_conjecture(m):\n", + " for n in count(1):\n", + " p = m - 2 * n^2\n", + " if p <= 0:\n", + " return False\n", + " \n", + " if is_prime(p):\n", + " return True\n", + "\n", + "\n", + "for k in count(2):\n", + " m = 2 * k - 1\n", + " if is_prime(m):\n", + " continue\n", + " \n", + " if not satisfies_conjecture(m):\n", + " break\n", + "\n", + "m" + ] + }, + { + "cell_type": "markdown", + "id": "dd35bb73", + "metadata": {}, + "source": [ + "Interestingly, the only other number known not to satisfy this conjecture is 5993." + ] + }, + { + "cell_type": "markdown", + "id": "3412975d", + "metadata": {}, + "source": [ + "## Relevant sequences\n", + "* Stern numbers (includes all odd numbers, not just composites): [A060003](https://oeis.org/A060003)" + ] + } + ], + "metadata": { + "kernelspec": { + "display_name": "SageMath 9.5", + "language": "sage", + "name": "sagemath" + }, + "language_info": { + "codemirror_mode": { + "name": "ipython", + "version": 3 + }, + "file_extension": ".py", + "mimetype": "text/x-python", + "name": "python", + "nbconvert_exporter": "python", + "pygments_lexer": "ipython3", + "version": "3.11.2" + } + }, + "nbformat": 4, + "nbformat_minor": 5 +}