Alex Landherr's repositories
amicable_sum
Evaluate the sum of all the amicable numbers under 10000.
bin_dec_palindrome
Find the sum of all numbers, less than one million, which are palindromic in base 10 and base 2.
circular_primes
How many circular primes are there below one million?
concat_prod
What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1, 2,...,n) where n > 1?
denom_val
Find the denominator of the product of the four non-trivial fractions when said product is expressed in its lowest common terms.
diagonal_spiral_sum
What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?
digit_sum
2^15 = 32768 and the sum of the digits is 3+2+7+6+8 = 26. What is the sum of the digits of the number 2^1000?
dist_terms
How many distinct terms are in the sequence generated by a^b for 2 ≤ a ≤ 100 and 2 ≤ b ≤ 100?
factorial_digit_sum
Find the sum of the digits in the number 100!.
factorial_sum
Find the sum of all numbers which are equal to the sum of the factorial of their digits.
fibonacci_digit_count
What is the index of the first term in the Fibonacci sequence to contain 1000 digits?
prime_threads
Multi-threaded benchmark in C++ that searches for prime numbers.
first_sum
Work out the first ten digits of the sum of the following one-hundred 50-digit numbers.
greatest_product
Find the thirteen (13) adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
grid_product
What is the greatest product of four adjacent numbers in the same direction (up, down, left, right or diagonally) in the 20x20 grid?
grid_routes
Starting in the top left corner of a 2x2 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 routes are there through a 20x20 grid?
longest_chain
Which starting number, under one million, produces the longest chain?
name_scores
What is the total of all the name scores in the file?
non_abundant_sum
Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers.
nth_permutation
What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?
nth_prime
What is the 10,001st prime number?
pandigital_prod_sum
Find the sum of all products whose multiplicand/multiplier/product identity can be written as a 1 through 9 pandigital.
pythag_trip
There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product abc.
square_dif
Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.
sum_below
Find the sum of all the primes below two million.
sum_of_powers
Find the sum of all the numbers that can be written as the sum of fifth powers of their digits.
sunday_count
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
triangle_num_divs
What is the value of the first triangle number to have over five hundred divisors?
triangle_path_sum
Find the maximum total from top to bottom of the triangle below (shown in 'prob18_image.png').
trunc_primes
Find the sum of the only eleven primes that are both truncatable from left to right and right to left.