Minecraft – Why is there a zombie that simply refuses to attack me

Where did the equation E = 3.5 * n * (n + 1) come from? I see that you say it came from the wiki, but I am unable to find it on there. I do see:

For any given level, the experience, E, required to achieve the next level n+1 from the current level, n is: E = 7 + roundDown(n * 3.5)

Thus, if you were level 0 you would require 7 experience to achieve level 1, which is not the case with E = 3.5 * n * (n + 1). To advance to level 2, you would need 10 more experience, a total of 17, not 14 more experience, with a total of 21. I hope that equation is not correct (because I just spent an hour on what I think is the correct one), and that would explain why you don't have to kill 1785 hostile mobs before level 50.

I've come up with E = 7n + round(3.5(.5(n^2)-.5n)) - n/4)

• E is the total experience needed to reach level n.

• "7n" accounts for the constant 7 experience required to reach every next level. This is the only experience you must collect to reach level 1. E = 7 + roundDown(n * 3.5)

• The ".5(n^2)-.5n" provides the number of 3.5 increments between level 0 and level n, but ignores the rounding down. Because the rounding down is not yet accounted for, I have "-n/4" (without this, the equation says you require one more experience than reality every 4 levels). E = 7 + roundDown(n * 3.5) Ex. Between levels 0 and 1 the number of required 3.5 experience increments is 0. Between 1 and 2 the number of 3.5 increments is 1. Between levels 2 and 3 the number of increments is 2. Between levels 0 and 3 the number of increments is 3. 0 + 1 + 2 = 3 3*3.5 is 10.5, and then 7*3 is 21. 10.5 + 21 is 31.5

• The "round()" rounds up some E values ending in .75 that result from the "-n/4". 31.5 - 3/4 = 30.75 round(30.75)= 31 And so you need 31 experience to reach level 3 from level 0.

With this equation, you require 4625 experience to reach level 50, which /5 is 925.

The answer you are looking for is hidden inside you own question: "there are a lot outside". The game randomly checks places to put mobs and since the outside is much larger than your trap, most of the zombie pigmen spawn there. The mob limit is exhausted pretty much instantly and the game doesn't spawn any more, unless some of the existing mobs de-spawn or get killed.

You will get zombie pigmen to spawn in your trap eventually, but you may have to wait hours for just a few spawns. You need to prevent spawning outside your trap to improve rates of your trap. This is very difficult to do in the nether, since you can't use light or water to prevent spawning. That is why you don't see zombie pigmen traps, building one is a monumental project. Notice for example here a huge area is covered with half-slabs to prevent spawning.

The spawnable area is +/- 8 chunks from each chunk where there is a player (minus the chunks on the edges of that area). If a single player is online, mobs spawn in 240x240 blocks area centered on the player chunk, that is roughly +/- 120 blocks from the player.