39+38+...+1 = 39*38/2 = 494
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Twelve: 2,3,5,7,11,13,17,19,23,29,31,37.
There are infinitely many pairs. The simplest to find is 1 and 40.
If you count 40 and 100, there's 61. 100-40+1=61
1,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25,26,27,28,30,32,33,34,35,36,38,39 are the composite numbers between 1 and 40.
5 / (1/8) = 5*8/1 = 40