Number preceding 10000 base 2

that's how you count in base 2 : P:

10001 10010 10011 10100 10101 10110 10111 11000 11001 11010 11011 11100 11101 11110 11111? see the pattern

or easier just convert to decimal = > decimal to bin

1 * 2^4 + 0 * 2^3 + 0 * 2^2 + 0 * 2^1 + 0 * 2^0 = 16

after 16 is 17 wow

so

17/2 = > (17 can't be divided over 2 without a reminder (8.5) or 1 is reminder)

8 (1) reminder

4 (0) reminder

2 (0) reminder

1 (0) reminder

0 (1) reminder (1 / 2 = 0.5 not a whole number always ends like that)

collect all reminders:

10001