[XPM] Primechain Origin

[busoni]

In Sunny's white paper, it says that the origin of a prime chain must be divisible by the block header hash. The language around here is a little confusing. Can someone tell me how, from the information in a given block (e.g. http://primecoin.21stcenturymoneytalk.org/index.php?block_hash=3605a3cfeca2cd5c8db539339f19e3b12185d60b93b79f28f6d1e35d91dcd252), I can get the number by which the origin of the next block must be divisible?