## pair

#### 1

The ordered pair $(a,b)$ can be chosen in 16 ways so as not to be a multiple of $(c,d)$.

There cannot be two edges between one pair of vertices.

#### 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 the 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