1
The ordered pair (a,b) can be chosen in 16 ways so as not to be a
multiple of (c,d).
2
Write out the integers from 1 to n. Pair up the first and the last,
the second and next to last, etc.
Go to List of words starting with:
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
Y
Z