= Common difference
{title2=$d=a_{k+1}-a_k$}
The common difference of an <arithmetic progression> is the fixed difference between consecutive <sequence terms>. It gives a <finite difference> that is independent of position. Checking one adjacent pair finds its value only when the <arithmetic progression> property is already known; otherwise, other pairs can disagree. For example, the differences in $7,10,14$ are three and four, so the three entries do not form an <arithmetic progression>.
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