When Google effectively splits its stock on Wednesday, S&P Dow Jones Indices will do something unprecedented: It will keep both the old Google shares and the new ones in the S&P 500. That means the will technically have 501 components, though it will still have only 500 companies.

"It's a good trivia question for everybody," Cowen & Co.'s head of sales trading, David Seaburg, said on last Thursday's episode of "Futures Now." "Next Wednesday, how many stocks are going to be in the S&P 500? It's 501!"

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On Wednesday, ahead of trading on Thursday, Google will offer shareholders nonvoting Class C shares as a one-time special dividend. Because there will be twice as many shares outstanding, the price of the shares is expected to fall in half, effectively making for a standard 2-for-1 stock split.

The move will not only decrease the plus-$1,000 price of Google's shares, but will also potentially reduce shareholders' voting power in the future, mitigating the risk of a messy fight with an activist investor who wants the company to distribute more cash (Carl Icahn's Apple fight might comes to mind).

In the past, S&P Dow Jones Indices, the company that runs the S&P 500, has not kept the additional shares that more than 40 S&P 500 companies offer in the index.

In fact, in a February press release, the company announced that it would switch Google from the Class A shares (which will trade under the ticker "GOOGL") to the class C shares (which will trade under the ticker "GOOG," and are likely to be more liquid).

But in a March press release, it revised that decision, and said both the Class A and Class C shares will be included in the S&P 500 (as well as in the S&P 100).

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This is the first time that more than 500 stocks will be included in the S&P 500 for anything more than a temporary period.