There is no simple formula for #a5a39c, but we have one for color #a49d86, that is similar to #a5a39c by 96.4%.
Color #a49d86 name: dark grayish khaki
Hex #a49d86 or rgb(164,157,134) in RGB space is the tint of khaki. It has hue angle of 46.00 degrees, value = 64 and saturation = 18. #a49d86 can be obtained by mixing 4 colors: 5 drops of yellow, 4 drops of magenta, 1 drop of blue, 4 drops of cyan.
Nearest safe hex - #999999. Below you can see the block with #a49d86 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #a49d86 to the mixer and play with it.