As the average number of patents per inventor is around 3, some sources define prolific inventors as five times above the average (in terms of patents), leading to a threshold of 15 patents.[355] However, this table currently has an arbitrary cut-off limit for inclusion of 200 patents. This is purely for practical reasons – there are tens of thousands of inventors with more than 15 patents. The threshold of 200 patents means that some famous prolific inventors such as Nikola Tesla are not included in this list, as Tesla had 111 patents.[356][357]