Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
f
n
=
b
-
n
+
-
1
+
a
n
l
o
g
a
-
1
+
a
i
n
v
e
r
s
e
Math Input
Natural Language
Math Input
