The Collaborative International Dictionary of English v.0.48:

alphanumerical \alphanumerical\ adj.
   1. of or pertaining to alphanumerics.

   Syn: alphanumeric, alphameric, alphamerical
        [WordNet 1.5]

   2. (Computers) using or consisting of only alphabetical and
      numerical characters; -- contrasting with binary or
      control. alphanumeric characters

   Syn: alphanumeric, alphanumerical, alphameric, alphamerical
        [PJC]

WordNet (r) 3.0 (2006):

alphanumerical
    adj 1: of or pertaining to alphanumeric characters [syn:
           alphanumeric, alphanumerical, alphameric,
           alphamerical]