18, 27, 36, 45, 54, 63, 72, 81, 90?
1, 10, 19, 28, 37, 46, 55 A-Ha!
81.
1
121
21 and 20
No two numbers that can be completely written down with digits can be added, subtracted, multiplied, or divided to equal PI. If they could be divided to equal PI, then PI would be a rational number. But it isn't.
412
A two digit number whose two digits added together equal 42 and multiplied together equal 82
55 52+52 = 50
Only if the final digit, after the decimal point, is zero.
1348.
The number is 36
25 & 36.