Math::Sequence defines a class for simple mathematic sequences with a 
recursive definition such as x_(n+1) = 1 / (x_n + 1). Creation of a 
Math::Sequence object is described below in the paragraph about the 
constructor.

Math::Sequence uses Math::Symbolic to parse and modify the recursive 
sequence definitions. That means you specify the sequence as a string 
which is parsed by Math::Symbolic. Alternatively, you can pass the 
constructor a Math::Symbolic tree directly.

Because Math::Sequence uses Math::Symbolic for its implementation, all 
results will be Math::Symbolic objects which may contain other variables 
than the sequence variable itself.

Each Math::Sequence object is an iterator to iterate over the elements of 
the sequence starting at the first element (which was specified by the 
starting element, the second argument to the new() constructor). It offers 
facilities to cache all calculated elements and access any element 
directly, though unless the element has been cached in a previous 
calculation, this is just a shortcut for repeated use of the iterator.

Every element in the sequence may only access its predecessor, not the 
elements before that.

WWW: http://search.cpan.org/dist/Math-Sequence/