If we take 47, reverse and add, 47 + 74 = 121, which is palindromic.

Not all numbers produce palindromes so quickly. For example,

349 + 943 = 1292,
1292 + 2921 = 4213
4213 + 3124 = 7337

That is, 349 took three iterations to arrive at a palindrome.

Although no one has proved it yet, it is thought that some numbers, like 196, never produce a palindrome. A number that never forms a palindrome through the reverse and add process is called a Lychrel number. Due to the theoretical nature of these numbers, and for the purpose of this problem, we shall assume that a number is Lychrel until proven otherwise. In addition you are given that for every number below ten-thousand, it will either (i) become a palindrome in less than fifty iterations, or, (ii) no one, with all the computing power that exists, has managed so far to map it to a palindrome. In fact, 10677 is the first number to be shown to require over fifty iterations before producing a palindrome: 4668731596684224866951378664 (53 iterations, 28-digits).

Surprisingly, there are palindromic numbers that are themselves Lychrel numbers; the first example is 4994.

How many Lychrel numbers are there below ten-thousand?

NOTE: Wording was modified slightly on 24 April 2007 to emphasise the theoretical nature of Lychrel numbers.

+-%run_procs
run_procs(wait,0,_,Val)->Val;
run_procs(wait,Running,AccFun,Val)->
	NextVal=receive Anything->Anything end,
	run_procs(wait,Running-1,AccFun,AccFun(Val,NextVal));
run_procs(HowMany,ArgFun,AccumulatorFun,InitialAccVal)->
	run_procs(1,HowMany+1,ArgFun,AccumulatorFun,InitialAccVal).
run_procs(Limit,Limit,_,AccFun,Val)->run_procs(wait,Limit-1,AccFun,Val);
run_procs(I,Limit,ArgFun,AccFun,Val)->
	[Mod,Fun,Args]=ArgFun(I),
	spawn(Mod,Fun,Args),
	run_procs(I+1,Limit,ArgFun,AccFun,Val).

+-%is_palindrome
is_palindrome(N)->
	S=integer_to_list(N),
	S == lists:reverse(S).

p55()->
	Ans=run_procs(9999,fun(I)->[euler,p55,[I,self(),0]] end,
			   fun(A,{done,true})->A+1;
			      (A,{done,false})->A end,0),
	io:format("~w~n",[Ans]).
p55(_,Parent,50)->Parent ! {done,true};
p55(N,Parent,Iter)->
	NN=N+list_to_integer(lists:reverse(integer_to_list(N))),
	case is_palindrome(NN) of 
		true->
			Parent ! {done,false};
		false->
			p55(NN,Parent,Iter+1)
	end.

+-#isPalindrome?
def isPalindrome?(n)
  s=n.to_s
  s==s.reverse
end

def p55
  tot=0
  (1...10000).each do |i|
    j=50
    n=i
    j-=1 while j>0 and not isPalindrome?(n+=n.to_s.reverse.to_i)
    tot+=1 if j==0
  end
  puts tot
end