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If you have a sequence with a constant first common difference, it can be defined using a linear equation. The following formula can be used to find any nth term in the sequence.

Where:

**a** is the first term in the sequence

**d** is the common difference between the terms

When you cannot find a constant first common difference, look at the second differences. If that second difference is constant, you can define the sequence using a quadratic equation. The following formula can be used to find any term in the sequence.

Where:

**a **is the first term in the sequence

**d** is the difference* between the first and the second term*

**c** is the common second difference you found.