Euler problem 27.2

Haskell

——————————

problem_27 = -(2*a-1)*(a^2-a+41)
    where n = 1000
          m = head $ filter (\x -> x^2 - x + 41 > n) [1..]
          a = m - 1 

This is the “official” Haskell solution to Euler problem 27.

This solution is incomprehensible. The following hints are as far as I can get.

Prerequisite considerations:

b must be a prime number, since x^2 + a*x + b must be a prime number when n=0.

a = m - 1 is a choice of the prime number b (in x^2 + a*x + b) just(?) smaller than 1000.


a == 32

(\x -> x^2 – x + 41) 31 == 971

Why not the prime number 997?

— Me@2015.06.14 08:53 AM

It is because 997 is not a prime number generated by the formula x^2 - x + 41.

— Me@2015-06-30 11:07:53 AM

map (\x -> x^2 - x + 41) [0..40]

is for generating 41 primes with the greatest Euler’s lucky number 41.

— Me@2015.06.14 08:34 AM

2015.07.01 Wednesday (c) All rights reserved by ACHK