Good thinking, but they don't do any file io, and I'm not sure how it could use less than a full CPU (wouldn't it just finish sooner? Though waiting for io could do that). OTOH it's java (on android, so dex format) and does some classloading of user classes... so maybe that is io? Here's time results:

  real    0m1.818s
  user    0m2.020s
  sys     0m0.900s

top. (It completes in 1 sec, so put in a while loop - BTW top isn't behaving normally, "1" not giving multiple CPUs and not fitting on screen). Jus the top line:

  User 51%, System 23%, IOW 0%, IRQ 0%