Kidney exchange time series

What is this sequence? 2, 4, 6, 19, 34, 27, 74, 121, 240, 304...

It is the number of "Non-Biol,unrel: Paired Exchange" kidney transplants in the OPTN database, i.e. the number of kidney transplants in which the donor was not a blood relative or married to the recipient, arranged by kidney exchange, in the years 2000-2009, by year. (Kidney exchange is also called paired kidney donation, kidney paired donation--KPD, and paired kidney exchange.)

Note the accelerating upward trend: the number of transplants through kidney exchange has grown by a factor of 9 since a comprehensive integration of living and deceased transplantations through both cycles and chains was proposed in 2004. For logistical reasons, the New England Program for Kidney Exchange (NEPKE) and the Alliance for Paired Donation (APD) initially started with exchanges between just two pairs. But soon larger exchanges and chains started to be commonplace, and today a nonnegligible part of the most recent growth is due to non-simultaneous chains.

The best practices seem to be spreading from hospital to hospital pretty well, organized by growing regional and other networks that coordinate exchanges. Sometimes there's some mis-coordination. There is still talk of a national exchange, although medical and other politics at a national level have so far raised some obstacles that need to be overcome.

In some moods I'm surprised that it has come so far so fast. In other moods I'm frustrated at how very slowly things have progressed. There's still lots of room to grow, and the need for kidney transplants keeps growing faster than the supply.

update: the OPTN data report requires a number of clicks once you get to their website, it is from the report "Living Donor Transplants By Donor Relation U.S. Transplants Performed : January 1, 1988 - February 28, 2010 For Organ = Kidney.
Starting from the web page http://optn.transplant.hrsa.gov/data/ , I choose “national data,” then choose category transplant, organ kidney, then click on Living Transplant by Donor Relation…