Integers come in two varieties -- fixnums and bignums. Fixnums fit in a machine word and are faster to manipulate; if the result of a fixnum operation is too large to fit in a fixnum, the result is upgraded to a bignum. Here is an example where two fixnums are multiplied yielding a bignum:
67108864 class-of . fixnum
128 class-of . fixnum
134217728 128 * . 17179869184
1 128 shift class-of . bignum
Integers can be entered using a different base; see Number syntax.
Integers can be tested for, and real numbers can be converted to integers: