The number of hobbyist-owned drones will reach 3.6 million by 2021, more than triple the 1.1 million last year, the Federal Aviation Administration said in a report last week.

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The FAA’s new predictions signal the general public’s increased interest in drones despite being a relatively new technology with only a handful of big vendors selling the flying robots.

In January, the FAA said that people had registered over 670,000 drones in 2016. The latest numbers, therefore, appear to be based on other sources and likely include unregistered drones. The FAA debuted a national drone registration system at the end of 2015.

In addition to data about hobbyist-owned drones, the FAA said that it expects roughly 442,000 drones to be used by businesses by 2021 for tasks like taking pictures of farmland or inspecting cell phone towers. That’s nearly ten times as many drones than the 42,000 the FAA said businesses used in 2016.

The FAA based its predictions for the commercial drone industry on the continuation of current drone regulations that prevent companies from flying drones at night or outside the line of sight of human operators. If regulations are significantly eased by 2021, the FAA projects businesses will use nearly 1.6 million drones.

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The FAA also said it expects the number of drone pilots to grow nearly 13-fold to 281,300 by 2021.