Some numbers remain numbers when turned upside down (using digits 0125689, with no final 0's):
1, 2, 5, 6, 8, 9, 11, 12, … etc
IF a1=1, a2=2, a3=5,... a8=12,…, etc
a.Evaluate a100
b. Evaluate a1000
c. If an= 888, what is n?