Time.com called it the 130 year old curse of the stock market, and it is referring to the unlucky 7. For full article, please refer to here. Why unlucky 7? If you looked at the historic of the US markets, during these periods of 2007, 1997, 1987 and 1907, these were the bear market with the biggest correction.
Expanding on the above, Dana Lyons, a partner at J.Lyons Fund Management wrote a blog post with the observation of the magnitude of the correction for each of these periods and more. You can read more of his blog post here.
Below is a tabulated extract from his post.