Read Numbers 2:16 Using Other Translations
All that were numbered in the camp of Reuben were an hundred thousand and fifty and one thousand and four hundred and fifty, throughout their armies. And they shall set forth in the second rank.
All those listed of the camp of Reuben, by their companies, were 151,450. They shall set out second.
So the total of all the troops on Reuben’s side of the camp is 151,450. These three tribes will be second in line whenever the Israelites travel.