We really need to understand the numeric relationships herein presented. If we add the cardinal numerals of 587 together (5+8+7) we arrive at 20. However, if we add the cardinal numerals of 586 (5+8+6) we arrive at 19, a prime number which cannot be created by multiplying two natural numbers together.
This is the same scenario presented when we look at the year 607 (6+0+7) and again arrive at a prime number, 13, which also cannot be created by multiplying two natural numbers together.
The unique aspect of 607 is that it contains a zero, which has been problematic due to the misunderstanding by many researchers since there is no zero year.
I can provide reference citations in APA 6th edition format if needed to support the analysis.
Rub a Dub