Alphabet to Number and Number to Alphabet Challenge

In this challenge you have to take a number as input and output the corresponding letter of the alphabet, and vice versa. (1 &lt;=> A, 2 &lt;=> B) etc.

1 -&gt; A
2 -&gt; B
...
26 -&gt; Z

A -&gt; 1
B -&gt; 2
...
Z -&gt; 26


Rules


This is code-golf, so shortest code in bytes wins.
The input will only consist of either an uppercase letter from A to Z or an integer from 1 to 26 inclusive.
Trailing whitespaces (space and newline) are allowed.
Pure Bash, 51
Most of the rest of the answers use some sort of conditional.  This one dispenses with conditionals entirely, and instead treats the input as a base-36 number which indexes into an appropriately constructed bash-brace-expansion array:
a=(_ {A..I} {1..26} {J..Z} {A..Z})
echo ${a[36#$1]}

Ideone.