Is 3.1214122144 an irrational number

No, this is a rational number.

It is 975,441,317/312,500,000.

In general, any number which has a decimal representation that either terminates (ends after some finite length) or repeats is a rational number (not an irrational one). Because this decimal expansion terminates, it is a rational number.

However, there are an infinite number of Irrational Numbers which begin with 3.1214122144.... Generally, we notate the approximation with the ellipses (...) and know we cannot record in a decimal form its exact value.

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