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