Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:

21 22 23 24 25
20  7  8  9 10
19  6  1  2 11
18  5  4  3 12
17 16 15 14 13

It can be verified that the sum of both diagonals is 101.

What is the sum of both diagonals in a 1001 by 1001 spiral formed in the same way?

p28()->p28(3,1).
p28(1003,T)->io:format("~w~n",[T]);
p28(N,T)->
	p28(N+2,T+lists:sum(lists:seq(N*N,N*N-3*(N-1),1-N))).

+-#Enumerable
module Enumerable
  def sum
    self.inject{|u,v|u+v}
  end
  def product
    self.inject{|u,v|u*v}
  end
  def count(ob)
    self.select{|i|i==ob}.length
  end
  def take_while
    return [] unless yield(self.first)
    if(self.class==Range)
      evalPoint=self.first
      evalPoint=evalPoint.succ while yield(evalPoint.succ) and not evalPoint==self.last
      return self.first..evalPoint
    else
      s=self.to_a
      upTo=1
      upTo+=1 while yield(s[upTo]) and upTo<self.length
      return self[0...upTo]
    end
  end
end

def p28
  sum=1
  (3..1001).step(2) do |i|

    sum+=(0..3).map{|j|i**2-j*(i-1)}.sum
  end
  puts sum
end