How many Americans in Japan are covered by Japanese pension?

Also: How many have been covered?

Does anyone know if the Japanese government publishes these kinds of figures? It goes to the totalization project. The piece I already have, from the other day, is that over 32,000 Japanese collect U.S. social security with the help of the totalization agreement. (There are any number more who qualified by getting the more-or-less 10 years (40 credits) that the States requires, as opposed to Japan’s 25 years.)

It doesn’t sound to me that the number of Americans participating in Japan would be a number that the Japanese would want to brag about. So I don’t expect to find it. But I do want to give the old college try–with your help!

[Update: Bonus points – how many Americans end up on SSI because they spent a lot of years in Japan, and never paid into the Japanese pension?]