For cables of the same diameter
There is a factor
1 cable Factor is 1
7 cables the factor is 3
19 cables the factor is 5
37 cables the factor is 7
61 cables the factor is 9
Cables all of the same diameter, formed around a central single core follow the "rule of 6"
the first layer is 6 plus the inner core is 7 (the 7 wire assembly is 3 cable diameters in diameter)
the second layer contains 6+6 plus the 7 below it, so it has 19 total cables and is 5 cable diameters in diameter.
The third layer is 6+6+6 or 18 cables plus 19.... and so on
hopes this helps
Wilber