The U.S. national debt was $2.9617 x 10^13 in 2021 and $3.98 x 10^11 aria-label

It appears there's a mix-up in the notation provided for the U.S. national debt figures. The figures should likely reflect larger amounts given the context of national debt.

As of 2021, the U.S. national debt was approximately **$29.617 trillion**, which can be expressed in scientific notation as **2.9617 x 10^13** dollars. This is indeed a correct representation.

However, the second figure you mentioned, "$3.98 x 10^11," seems to be a mistake. It represents approximately **$398 billion**, which is an order of magnitude lower than what the national debt would typically indicate during that timeframe.

If you have specific updates or a year you are referring to, please clarify so I can assist you better!