The pattern goes
square, add 2, subtract 1,
square, add 2, subtract 1,
square, add 2, subtract 1,
etc., etc., etc.
Start with 1
Square 1, get 1
add 2, get 3
subtract 1, get 2
Square 2, get 4
add 2, get 6
subtract 1, get 5
Square 5, get 25
add 2, get 27 <--- that's the answer!
subtract 1, get 26
Square 26, get 676
add 2, get 678
subtract 1, get 677
Edwin