Paul starts at 1 and counts by threes: 1, 4, 7, 10, . . . . At the same time and at the same speed, Penny counts backwards from 2017 by fives: 2017, 2012, 2007, 2002, . . . . Find the one number that both Paul and Penny count at the same time.

Source: Purple Comet 2017

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