Have you ever wondered which sequences of two letters don't appear in any words in the English language? Then you're in the right place
( for a in {a..z}; do for b in {a..z}; do grep -q $a$b /usr/share/dict/words || echo $a$b ; done; done if you want your very own list):
bq
bx
bz
cf
cg
cj
cp
cv
cw
cx
dx
fq
fv
fx
fz
gv
gx
hx
hz
jb
jc
jd
jf
jg
jh
jj
jl
jm
jn
jp
jq
jt
jv
jw
jx
jy
jz
kq
kv
kx
kz
lx
mg
mj
mx
mz
pq
pv
px
qc
qd
qe
qf
qg
qh
qj
qk
ql
qm
qn
qo
qp
qq
qr
qs
qt
qv
qw
qx
qy
qz
sx
tq
tx
vb
vc
vf
vj
vk
vm
vp
vq
vw
vx
vz
wj
wq
wv
wx
xd
xj
xk
xm
xr
yq
zf
zj
zx