I was with the dar on Yom Kippur, and they were using the Silverman machzor, but I was using my Koren machzor, but also occasionally referring to the Silverman when I needed to figure out where we were.
The Silverman machzor includes both Rosh Hashanah and Yom Kippur, so Yom Kippur begins on page 191 and goes to page 499. The Koren is only Yom Kippur, so YK begins on page 1. But it's a smaller book, with less on each page, so YK goes all the way to page 566. Thus, I noticed that the page numbers in the Koren are lower at the beginning of YK, but higher by the end. If each mapping of prayers to page numbers is a continuous monotonic function, this means that there must be a point of intersection, some prayer that is on the same page in both books!
So I set out to find what it was, knowing that this prayer where everything is aligned must have some special significance. Sure enough, on page 359 in both the Silverman and the Koren is... the musaf kedusha!!! The highest point of the whole day!!!!
So then I figured that there must be a comparable cosmic numerical confluence on Shavuot, because it has been suggested that Shavuot and Yom Kippur are parallel holidays: Yom Kippur is when the individual stands before God, while Shavuot is when the nation collectively stands before God.
I looked at my watch yesterday and saw that the secular date of Shavuot this year was June 13! 6-13! 613!!!!! 613!!!!!!!!!!!!