It took Satoshi Nakamoto 6 days to come up with a mechanism to attribute coins mined to an entity. Today this entity is known as 'Bitcoin address' and is considered to work as an account. In the first days of the Bitcoin though, the intended use of an address was that of an invoice - hence the official name: invoice address.

The invoice address concept works in this way: the miner is issuing an invoice to be paid by the network, as compensation for mining. The network coin generation mechanism creates the agreed coins, and pays the miner.

That day, Satoshi Nakamoto added the first 14 usable blocks, in 99 minutes, using his personal computer. Each block took from 79 to 815 seconds. It was simply a test run, to check whether the blockchain (Nakamoto was using the term time chain, since reference hashes were time-based) was working as expected, how long it takes to mine a block, if invoices are correctly paid, etc.

Here are the first invoice addresses created by Satoshi Nakamoto:

12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX

1HLoD9E4SDFFPDiYfNYnkBLQ85Y51J3Zb1

1FvzCLoTPGANNjWoUo6jUGuAG3wg1w4YjR

15ubicBBWFnvoZLT7GiU2qxjRaKJPdkDMG

1JfbZRwdDHKZmuiZgYArJZhcuuzuw2HuMu

1GkQmKAmHtNfnD3LHhTkewJxKHVSta4m2a

16LoW7y83wtawMg5XmT4M3Q7EdjjUmenjM

1J6PYEzr4CUoGbnXrELyHszoTSz3wCsCaj

12cbQLTFMXRnSzktFkuoG3eHoMeFtpTu3S

15yN7NPEpu82sHhB6TzCW5z5aXoamiKeGy

1dyoBoF5vDmPCxwSsUZbbYhA5qjAfBTx9

1PYELM7jXHy5HhatbXGXfRpGrgMMxmpobu

17abzUBJr7cnqfnxnmznn8W38s9f9EoXiq

1DMGtVnRrgZaji7C9noZS3a1QtoaAN2uRG

Satoshi though needed to solve several issues: how transactions other than mining rewards would be entered in each block? What if the invoice owner needed to send fewer than the whole 50 bitcoins attributed to the invoice address? The mining application needed a few modifications, before he could invite others to start doing test mining.