Question

What number is needed to complete the pattern 66, 73, 13, 21, 52,_, 10, 20?

Answer 1

66,73 73-66=7
13,21 21-13=8
10,20 20-10=10

the missing no. is 9 so
52+9=61.

the pattern is
66,73,13,21,52,61,10,20