Back in 2009 a group of Silicon Valley investors cut Square a $10 million check.

It was venture capital in its purest form: A risky bet on an unproven technology. The odds of Square being successful were long. The entire nation was in the depths of a severe recession. And Square’s technology was centered on a small, white, square-shaped card reader that no one knew much about.

So Square’s co-founders Jack Dorsey (of Twitter fame) and Jim McKelvey looked to private investors in Silicon Valley willing to buy a stake in the new company.

There were 19 investors in that first Series A financing round, according to Crunchbase. The $10 million investment was led by Khosla Ventures, which focuses on early-stage companies. Other investors included Biz Stone, co-founder of Twitter; Dennis Crowley, co-founder of Four Square; Silicon Valley veteran Esther Dyson; Marissa Myer, who worked at Google and would go on to lead Yahoo; and Kevin Rose, founder of Digg who would go to join Google Ventures.

That gave the investors shares priced at just under 22 cents each.

According to documents filed ahead of Square’s initial public offering, the Series A investors had about 46.7 million shares.

On Thursday, Square’s stock debuted on the public markets.

The price started at $9 a share, which was below the value given to investors in the last financing rounds.

But by day’s end, Square stock ended at $13.07 – a 45% increase.

For those earliest investors, stock they had purchased for .21627 cents (to be exact) back in 2009 was now worth 60 times as much. There is some slight variability in that number, depending on how some of the financing was structured.

Overall, that $10 million investment today is worth $604 million.