Can you solve this?

[Luke]

[spoiler][/spoiler]

/thread.

Or not really. I'm melting my brain on this and I don't get it (that awkward moment when you realize 'I'm a dumbass'. Ahah!).

Do you know this problem? Can you solve it?

I ask everyone to don't write the solution; if you do put it between a spoiler tag, please.

[Miruku]

I have never seen it before, nor do I have an idea what is going on there.

[skyrimguy]

Really hard riddle!?

[agaures]

2581 = 2

[Cruduxy]

heh this very old riddle again.. "I would tell him the answer is 2 because it means how many circles are in the numbers. :) "
Only reason kids solve it fastest is because they don't damage their brain over-thinking stuff

[Kara Kurt]

Got the answer I feels smarter now.

[ibm5155]

It's a lie, I'm a programmer and I did it in one minute ¬¬
[spoiler]0=1
1=0
2=0
3=0
4=?
5=0
6=1
7=0
8=2
9=1

replace the number by the other number then add all
ex: 9999 -> 1111 -> 1+1+1+1=4
so the awnser is 2[/spoiler]

[agaures]

It's a lie, I'm a programmer and I did it in one minute ¬¬
[spoiler]0=1
1=0
2=0
3=0
4=?
5=0
6=1
7=0
8=2
9=1

replace the number by the other number then add all
ex: 9999 -> 1111 -> 1+1+1+1=4
so the awnser is 2[/spoiler]

Exactly how i worked it out.

[Luke]

heh this very old riddle again.. "I would tell him the answer is "
Only reason kids solve it fastest is because they don't damage their brain over-thinking stuff

thanks for the spoiler eh

[Nati46]

Number of closed "holes" in each number :)
(so 2581 = 2)
Just realises those above me figured this out, although in a more analytic way

[Ivan]

I've seen worse. (Linear Algebra says hi)