Answer
arithmetic
Work Step by Step
An arithmetic sequence may be defined recursively as
$a_{1}=a,$
$a_{n}-a_{n-1}=d$
or as
$a_{1}=a\quad $
$a_{n}=a_{n-1}+d$
where $a_{1}=a$ and $d$ are real numbers.
The number $a$ is the first term, and
the number $d$ is called the common difference.
Fill the blank with: arithmetic
