What's the difference between long unsigned int and unsigned long int

They are the same.

Quote C11

, chapter §6.7.2, Type specifiers (emphasis)

List:

type specifier:

void

char

short

int

long

float

double

signed

unsigned

_Bool

_Complex

atomic-type specifier

structure or union-specifier

enum specifier

Breece name

and, P2,

The declaration specifiers in each declaration include at least one type specifier, and in the specifier-specifier list in each structure declaration and type name. Each list of type specifiers must be one of the following multisets (comma separated when more than one multiset per element); type specifiers can appear in any order, possibly mixed with other declaration specifiers.