@thatch45 me and @techhat discussed this above. It should have an "n". According to a top hit on Google (http://www.grammar-monster.com/lessons/an_or_a.htm): 

"There is sometimes confusion about whether to use an or a (particularly with abbreviations). The sound of a word's first letter determines which to use. If the word starts with a vowel sound, you should use an. If it starts with a consonant sound, you should use a."