Security to the Party [Part 25]

Question

Another time, there is still another never-ending party at a local mansion. The host is very rich and his success is because of one thing ~ his famous recipes for spaghetti, fettuccini, green salad and juice!

The only guests that may attend are people the host knows and trusts, whom he gave the password to enter to.

Here's where you come in. You and four friends are trying to steal this recipe. This time you called four friends to get many heads working simultaneously to quickly break the code. To successfully steal it, two people are needed to simultaneously rotate two keys on a vault inside the mansion. You all sneak by and listen to the passwords.

The first guest arrives. The security says "19", and the guest replies "3".

The second guest arrives. The security says "14", the guest replies "3".

The third guest arrives. The security says "9", the guest replies "3".

Your friend #1 quickly goes there, that is the easiest password afterall! The security says "20" and he replies "3". Immediately an elephant falls from the sky over him and starts to dance over his crushed body splattering blood.

Another guest arrives. The security says "15", the guest replies "1".

Still another guest arrives. The security says "22" and the guest replies "22".

Your other three friends looked one to the other at the same time, smiled, and the friend #2 said:

"Are you pondering what I am pondering?"

The other two friends answered together at the same time:

"I think so, Brain".

Your friends goes there. The guard asks "21" to your friend #2. He quickly happily answers "4" and goes inside. Good, now you just need just one more man!

Now, your friend number #3: The guard asks "31". Your friend immediatelly freezes in panic and becames mute. The guard impaciently repeats: "31". Your friend starts to sweat and to cry without answering. So the guard had no other option but to kill -9 your friend.

Finally, your friend number #4: The guard asks "25". He stops, thinks, thinks, thinks and in the end he says: java.lang.StackOverflowError and explodes.

Darn, now you are the last guy available.

You see another guest coming. The guard asks "24". The guest answers "9".

You decided to go there. The guard asks "11". What should you answer? Explain why. Why your friends #3 and #4 failed? Please put your answer inside spoiler tags.

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Since we already got 2 very wrong answers, here some hints:

Hint 1:

31 can't be answered (but you still should tell me why).

Hint 2:

The computation for 25 can recurse forever. Tell me why.

Hint 3:

The answer for 20 was wrong. It is not 3.

Hint 4:

You could look to this question all day long and do a lot of math just to go to nowhere. You will need to look somewhere outside to find the answer and to understand why the answers given by the guests are correct.

Hint 5:

Don't need to go to wikipedia. The links in the start are just a joke.

Hint 6:

No math is needed to solve this.

Hint 7:

This is not a wording or letters gameplay.

Answer 1

Answer is 9

Because

The security to the Party part 19 answer 3 The security to the Party part 22 answer 22 The security to the Party part 24 answer 9

So that

The security to the Party part 11 answer 9. Now no part in 31. so now no answer for 31

4th Friend

I think if friend check 25 part that part itself again asking same question so it recursively so it so error

Answer 2

OK, my answer is this:

Say any number and try to avoid being squashed by falling animals.

Because:

The guards have been instructed to say a number to anybody who tries to enter, and to admit anybody who replies numerically. There is an problem with falling animals in the area where the party is being held - this is entirely unrelated to the party entry system, except that of course any guests killed by falling animals are no longer welcome at the party. (If they had loads of corpses at the party, that might spoil everybody's enjoyment.)

Answer 3

The mansion is actually a MCC LAD system (take the capital letters from the recipe links) and the numbers the guard said were signals sent by the system. Following the standard UNIX signals' chart, signal 11 corresponds to "segfault", so an appropriate answer would be 9, "kill" signal. #4 failed because he continued his thinking activity until a stackoverflow error raised (25 is "continued"), #3 could've stand the size of the input so he didn't know how to manage it, being killed by a "kill -9" sent by the system. Everything is related with Unix signals.