I have a spreadsheet and in column A a series of numbers all the same length
example:

412381

412382

412383

412384

412385

412386

412387

I need to iterate through and insert : between the second and third digit
and fourth and fifth. The outcome should resemble the following:

41:23:81

41;23;82

41;23;83

41;23;84

41;23;85

41;23;86

41;23;87

How does one accomplish this? Thanx.