Proton NMR question

So this might be a silly question but
Let’s say you have butane [CH3CH2CH2CH3].
One proton environment will have 6 hydrogens (the two CH3’s). When looking at the number of hydrogens in neighbouring environment (to determine the splitting pattern), should I add all the hydrogens (each CH3 is neighbouring a CH2, totalling 4 hydrogens) or should I look at one of the neighbouring environments (only one CH2, would total to 2 hydrogens)?

Butane is a weird one.
It’s symmetrical and so both of the CH3’s are equivalent to each other and the two CH2’s are equivalent, so you have two signals - perfectly normal so far.
The CH3’s both split into triplets because they are adjacent to two non-equivalent protons (each in the form of CH2’s) - again, perfectly normal.
So why have I called butane weird? Well, let’s look at the splitting of the two CH2’s. By the simple definition of the n+1 rule you are taught, you’d say each CH2 is adjacent to 5 hydrogens and so should split into a sextet, but what actually happens is you get a quartet.
The actual definition of the n+1 rule is that a signal is split n+1 times where n is the number of non-equivalent, adjacent protons. Whilst the CH2’s are each adjacent to 5 hydrogens, only 3 are non-equivalent (since the CH2’s are chemically equivalent). This is why you get a quartet and not a sextet.
But what about if you have something like butan-1-ol, CH3CH2CH2OH? Simply put, because one CH2 is adjacent to a CH3 and the other is adjacent to an OH, they are not equivalent. Hence the CH2 between the CH3 and the other CH2 splits to give a sextet and the other CH2 splits to give a triplet (-OH hydrogens are weird - you could say hydrogens bound to carbon can’t “see” them and so they don’t affect the splitting).