It is 39*n+1 when divided by n, for any integer n.
79 - 39 = 40
40
The solution to 79 plus 39 is 118. The solution to 79 minus 39 is 40.
79 x .39 = 30.81%
79
0.3911
79
2.4688
If you mean 29, 39, 59 and 79 then it is 39 that is the only composite number.
0.0001
79