It took a while, but Sirius XM Radio (Nasdaq: SIRI) is finally being added to the Nasdaq 100 composite.

Teva Pharmaceutical's (Nasdaq: TEVA) pending acquisition of Cephalon (Nasdaq: CEPH) is creating an opening in the popular metric of secondary stocks, and the satellite radio operator certainly has the girth to be considered a proxy for the exchange.

Despite the low share price, there are only a small handful of companies that have as many shares outstanding. Sirius XM has the equivalent of 6.5 billion shares after baking in Liberty Capital's (Nasdaq: LCAPA) 40% preferred share stake  

Sirius XM commands a market cap of more than $14 billion, and a chunky debt-adjusted enterprise value of roughly $17 billion. Don't let Sirius XM's miniscule share price fool you. This is a huge company that's routinely among the market's most actively traded stocks.

What kind of an impact will this have on Sirius XM heading into Friday morning's induction? Well, there will definitely be some institutional buying by index fund managers, though it goes without saying that this isn't a gauge that mutual funds ape the way they do the S&P 500.

It will be interesting to see if the move triggers a short squeeze. Sirius XM isn't just an actively swapped stock that has rewarded bulls with a huge two-year run. There were also nearly 300 million shares sold short as of mid June. Then again, given the sheer volume of Sirius XM shares traded daily, this only amounts to a short interest ratio of a little more than three days.

It's an honor that's long overdue for the volatile satellite radio star. Proof that Sirius XM has been a gruesome oversight in the index is obvious now: Sirius XM wouldn't be in the Nasdaq 100 by the end of this week if Cephalon hadn't been acquired, yet Cephalon is being snapped up for less than half of Sirius XM's market cap.

How high will Sirius XM move this week in anticipation of the index inclusion? Share your thoughts in the comment box below.

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Longtime Fool contributor Rick Munarriz is a subscriber to Sirius since 2004. He does not own shares in any of the stocks in this article. He is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance.