Integer Integer is the head for the atomic integer type. Attributes[Integer] := {Protected} Simple examples In[1]:= Head[153] Out[1]= Integer Integer numbers are backed by arbitrary-precision data structures: In[2]:= Factorial[40] Out[2]= 815915283247897734345611269596115894272000000000 Further examples In[1]:= MatchQ[153, _Integer] Out[1]= True