The Collaborative International Dictionary of English v.0.48:

Arithmetical \Ar`ith*met"ic*al\, a.
   Of or pertaining to arithmetic; according to the rules or
   method of arithmetic.
   [1913 Webster]

   Arithmetical complement of a logarithm. See Logarithm.

   Arithmetical mean. See Mean.

   Arithmetical progression. See Progression.

   Arithmetical proportion. See Proportion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arithmetical
    adj 1: relating to or involving arithmetic; "arithmetical
           computations" [syn: arithmetical, arithmetic]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "arithmetical":
   algebraic, algorismic, algorithmic, aliquot, analytic, cardinal,
   decimal, differential, digital, even, exponential, figural,
   figurate, figurative, finite, fractional, geometric, imaginary,
   impair, impossible, infinite, integral, irrational, logarithmic,
   logometric, mathematical, negative, numeral, numerary, numerative,
   numeric, odd, ordinal, pair, positive, possible, prime, radical,
   rational, real, reciprocal, submultiple, surd, transcendental