It's a big week for bitcoin — and for pizza.

Monday marked Bitcoin Pizza Day — the date seven years ago when Laszlo Hanyecz completed the first ever purchase with bitcoin. Hanyecz bought two pizzas for 10,000 bitcoin, a quantity of the cryptocurrency that is now worth more than $21 million.

Bitcoin aficionados use that milestone every year to track the growth of the cryptocurrency.

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While bitcoin's value has grown astronomically since 2010, its price is at an especially high peak right now. On Tuesday morning, one bitcoin was valued at $2,245, according to CoinDesk. That one bitcoin today could buy you more than 100 $20 pizzas — let alone what the 10,000 bitcoins Hanyecz spent in 2010 could buy. That amount of the cryptocurrency was then valued at $41.

Hanyecz's pizza purchase was a big deal because no mainstream retailers accepted bitcoin as a form of payment at the time. He couldn't buy pizza directly with bitcoin, so he traded his 10,000 bitcoins to another user in exchange for the two pizzas.

In the wild west days of bitcoin, the cryptocurrency was used for pizza and for illicit purchases (mostly drugs) on the online black market Silk Road.

Now, you can use bitcoin to pay for a Subway sandwich. Or pizza!