Arriving at Annuity (PV / df)

Question:
PV at 10%
0 Cost $1.500,000 in 5 years * df 0.621 = $ 931,500

0-4 Annuity * (1+df @ 10%) = $ 931,500

0-4 Annuity = $ 931,500 / (1+df @ 10%)

0-4 Annuity = $ 931,500 / (1+3.170)

0-4 Annuity = $ 931,500 / 4.170 = 223,381

Why is there a 1+ on the discount factor? …the df 0-4 at 10% +1? why +1?
this is revision kit question 104 answer on page 127.
Thanks in advance.