John Gill Commentary Numbers 2:6

"And his host, and those that were numbered thereof, were fifty and four thousand and four hundred." — Numbers 2:6 (ASV)

And his host
The host of Issachar;

and those that were numbered thereof, [were] fifty and four thousand
and four hundred .
.] 54,400 men. They had been numbered, for it does not appear that there was a fresh account taken; see (Numbers 1:29) .