The quantity which, when the diameter is multiplied by it, yields the circumference

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Across
  1. 4. Pi also has another name, after an ancient Greek mathematician
  2. 5. This famous physicist was born today
  3. 6. What type of number is pi?
  4. 7. The first 36 digits of pi has this name, after a German-Dutch mathematician that calculated the numbers during most of his life
  5. 8. A suggested alternative to pi, which equals 2 times pi, and is supposedly more intuitive to use for some math applications
  6. 9. The symbol for pi was introduced by William Jones, a Welsh mathematician, in 1706, but it was made more widely popular by this mathematician.
Down
  1. 1. The last man on the moon (so far) was born today
  2. 2. This man from Vellore, India, memorized the first 70,000 digits of pi
  3. 3. This science museum in San Francisco started the celebration of pi day in 1988