All Amex cards start with 37
ab is tied to the country of issuance/market
cd usually relates to the product in the AmEx portfolio
e is billing cycle
fghi is account number
j is the issue number
kl are position on the account, starting with 00 for the main (basic) card holder
m is the Luhn/mod 10 check digit"
"Problem is, I think users tend to think “globally.” They expect all activity within a space or context to be visible to them. If a search for some user can return nothing because the subject is outside your local social graph, then your technology is less useful than other search models. This is why we tend to pool around well-maintained global indexes to give reliable results, but then you have centralized authority emerging."