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原创 Circular primes

https://projecteuler.net/problem=35Circular primesProblem 35The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.The

2016-04-27 22:14:11 412 1

原创 Digit cancelling fractions

https://projecteuler.net/problem=33Digit cancelling fractionsProblem 33Published on Friday, 20th December 2002, 06:00 pm; Solved by 47920; Difficulty rating: 5%The fraction 49/98 is a curious frac

2016-04-24 21:54:24 428

原创 Coin sums

https://projecteuler.net/problem=31Coin sumsProblem 31In England the currency is made up of pound, £, and pence, p, and there are eight coins in general circulation:1p, 2p, 5p, 10p, 20

2016-04-10 17:17:03 386

原创 Digit fifth powers

https://projecteuler.net/problem=30Digit fifth powersProblem 30Surprisingly there are only three numbers that can be written as the sum of fourth powers of their digits:1634 = 14 + 64

2016-04-10 11:11:11 298

原创 Distinct powers

https://projecteuler.net/problem=29Distinct powersProblem 29Consider all integer combinations of ab for 2 ≤ a ≤ 5 and 2 ≤ b ≤ 5:22=4, 23=8, 24=16, 25=3232=9, 33=27, 34=81, 35=243

2016-04-10 10:56:52 465

原创 Number spiral diagonals

https://projecteuler.net/problem=28Number spiral diagonalsProblem 28Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:21

2016-04-02 17:42:16 343

原创 Quadratic primes

https://projecteuler.net/problem=27Quadratic primesProblem 27Euler discovered the remarkable quadratic formula:n² + n + 41It turns out that the formula will produce 40 primes for

2016-04-01 22:28:39 410

原创 Reciprocal cycles

https://projecteuler.net/problem=26Reciprocal cyclesProblem 26A unit fraction contains 1 in the numerator. The decimal representation of the unit fractions with denominators 2 to 10 are

2016-03-30 14:35:04 546

原创 Lexicographic permutations

https://projecteuler.net/problem=24Lexicographic permutationsProblem 24Published on Friday, 16th August 2002, 06:00 pm; Solved by 75662; Difficulty rating: 5%A permutation is an ordered

2016-03-22 13:44:58 634

原创 Non-abundant sums

https://projecteuler.net/problem=23Non-abundant sumsProblem 23A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum o

2016-03-22 13:05:17 317

原创 Amicable numbers

https://projecteuler.net/problem=21Amicable numbersProblem 21Let 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

2016-03-05 19:03:24 465 1

原创 Counting Sundays

https://projecteuler.net/problem=19Counting SundaysProblem 19You are given the following information, but you may prefer to do some research for yourself.1 Jan 1900 was a Mon

2016-03-05 16:28:05 326

原创 Maximum path sum I

https://projecteuler.net/problem=18Maximum path sum IProblem 18By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to

2016-03-04 15:29:42 186

原创 Lattice paths

Lattice pathsProblem 15Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom right corner.How many such

2016-03-04 09:01:24 393

原创 Longest Collatz sequence

https://projecteuler.net/problem=14The following iterative sequence is defined for the set of positive integers:n → n/2 (n is even)n → 3n + 1 (n is odd)Using the rule above and startin

2016-03-03 22:43:33 467

原创 https://projecteuler.net/problem=12

Highly divisible triangular numberProblem 12The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. T

2016-03-01 10:26:43 294

原创 https://projecteuler.net/problem=11

In the 20×20 grid below, four numbers along a diagonal line have been marked in red.08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 0849 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56

2016-02-28 21:52:55 244

原创 https://projecteuler.net/problem=10

Summation of primesProblem 10The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.Find the sum of all the primes below two million.此题就是考察素筛法，如果一个一个算，没太大必要primelist = [True]

2016-02-25 14:36:41 277

原创 https://projecteuler.net/problem=9

Special Pythagorean tripletProblem 9A Pythagorean triplet is a set of three natural numbers, a b <c, for which,a2 + b2 =c2For example, 32 + 42 = 9 + 16 = 25 = 52.There exists exact

2016-02-25 14:26:24 276

原创 https://projecteuler.net/problem=8

Largest product in a seriesProblem 8The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.7316717653133062491922511967442657474235534919

2016-02-24 20:57:36 320

原创 https://projecteuler.net/problem=7

10001st primeProblem 7Published on Friday, 28th December 2001, 06:00 pm; Solved by 257306; Difficulty rating: 5%By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see

2016-02-24 20:33:28 233

原创 https://projecteuler.net/problem=6

Sum square differenceProblem 6The sum of the squares of the first ten natural numbers is,12 + 22 + ... + 102 = 385The square of the sum of the first ten natural numbers is,(1 + 2 + .

2016-02-23 21:29:44 223

原创 https://projecteuler.net/problem=5

欧拉问题集，第五题，最小公倍数Smallest multipleProblem 52520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.What is the smallest positive num

2016-02-23 21:11:34 281

原创 https://projecteuler.net/problem=4

Largest palindrome productProblem 4A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.Find the largest pal

2016-02-23 13:29:32 289

原创 https://projecteuler.net/problem=3

Largest prime factorProblem 3The prime factors of 13195 are 5, 7, 13 and 29.What is the largest prime factor of the number 600851475143 ?当时考虑最大质因子，只要拿这个数自最小的质数开始除，除到最后，剩下的就是最大的质因子了，结果写出来

2016-02-23 09:10:22 237

今天下班回家的路上，开车在小路上50KM/H左右，眼睛一直在盯着前方的车，突然发现一只黑猫飞跑过来，在前方2m，左侧1-2m之间，当时感觉急刹车来不及了，没有急刹车，向右打了一下方向盘，感觉碰到了东西，就赶紧向左打了一下方向盘，就开过去了，没停车就直接过去了。过去之后看到后面有一辆车停下来了，极有可能猫被我压死了。好可怜呀，最近开车一直都太放松了，没有关注这些小动物，导致出了这样的悲剧。如果这只猫

2016-02-18 22:57:23 1210 1

原创 https://projecteuler.net/problem=2

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...By considering the

2016-02-14 15:15:54 256

原创 https://projecteuler.net/problem=1

自己做题玩If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.Find the sum of all the multiples of 3 or 5 below 1000.

2016-02-14 13:52:04 249

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