# Project Euler

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*projecteuler.net*. Accessed Feb 19, 2023.

Dated Jan 7, 2022; last modified on Fri, 07 Jan 2022

Archived Problems - Project Euler*.*
*projecteuler.net* .
Accessed Feb 19, 2023.

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Jan 7, 2022 | » | 019. Counting Sundays
6 min; updated Jan 7, 2022
Problem Statement You are given the following information, but you may prefer to do some research for yourself: 1 Jan 1900 was a Monday. Thirty days has September, April, June and November. All the rest have thirty-one, Saving February alone, Which has twenty-eight, rain or shine. And on leap years, twenty-nine. A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.... |

Jan 15, 2022 | » | 020. Factorial Digit Sum
4 min; updated Jan 15, 2022
Problem Statement \(n!\) means \(n \times (n - 1) \times … \times 3 \times 2 \times 1\). For example, \(10! = 10 \times 9 \times … \times 3 \times 2 \times 1 = 3628800\), and the sum of the digits in the number \(10!\) is \(3 + 6 + 2 + 8 + 8 + 0 + 0 = 27\). Find the sum of the digits in the number \(100!... |

Feb 6, 2021 | » | 021. Amicable Numbers
8 min; updated Feb 6, 2021
Problem Statement Let \(d(n)\) be defined as the sum of proper divisors of \(n\) (numbers less than \(n\) which divide evenly into \(n\)). If \(d(a) = b\) and \(d(b) = a\), where \(a \neq b\), then \(a\) and \(b\) are an amicable pair and each of \(a\) and \(b\) are called amicable numbers. For example, the proper divisors of \(220\) are \(1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110\); therefore \(d(220) = 284\).... |

Feb 18, 2022 | » | 022. Name Scores
5 min; updated Feb 18, 2022
#22 Names scores - Project Euler. projecteuler.net . Accessed Feb 18, 2022. Problem Statement Using names.txt, a 46K text file containing over 5,000 first names, begin by sorting it into alphabetical order. Then working out the alphabetical value for each name, multiply this value by its alphabetical position in the list to obtain a name score. For example, when the list is sorted into alphabetical order, COLIN, which is worth \(3 + 15 + 12 + 9 + 14 = 53\), is the 938th name in the list.... |

Feb 19, 2023 | » | 023. Non-Abundant Sums
9 min; updated Feb 19, 2023
#23 Non-abundant sums - Project Euler. projecteuler.net . Accessed Feb 19, 2023. Problem Statement A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of \(28\) would be \(1 + 2 + 4 + 7 + 14 = 28\), which means that \(28\) is a perfect number.... |

TIL Project Lovelace , which is like Project Euler, but instead of number theory, their problems are broader, e.g., astronomy, ecology, statistics, genetics, etc. As of Feb 2023, they have 28 problems, with the problem #28 being uploaded back in 2019.