摘要：Lexicographic permutationsProblem 24A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation ... 阅读全文

摘要：Counting SundaysProblem 19You are given the following information, but you may prefer to do some research for yourself.1 Jan 1900 was ... 阅读全文

摘要：Number letter countsProblem 17If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + ... 阅读全文

摘要：Square digit chainsProblem 92A number chain is created by continuously adding the square of the digits in a number to form a new numbe... 阅读全文

摘要：Prime-Sum NumbersProblem 543Define function P(n,k) = 1 ifn can be written as the sum of k prime numbers (with repetitions allowed), an... 阅读全文

摘要：Largest exponentialProblem 99Comparing two numbers written in index form like 211 and 37 is not difficult, as any calculator would con... 阅读全文

摘要：Amicable numbersProblem 21Let d(n) be defined as the sum of proper divisors ofn (numbers less thann which divide evenly into n).If d(a... 阅读全文

摘要：1000-digit Fibonacci numberProblem 25The Fibonacci sequence is defined by the recurrence relation:Fn = Fn−1 + Fn−2, where F1 = 1 and F... 阅读全文

摘要：Factorial digit sumProblem 20n! means n × (n − 1) × ... × 3 × 2 × 1For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,and the sum o... 阅读全文

摘要：Maximum path sum IIProblem 67By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum... 阅读全文