convert number (integer) into hour:minute:seconds

I am trying to convert a column of numbers into hours:minutes:seconds.

For example, I have following numbers (original data followed by desired output). I tried using the custom number format but could not get the desired result. Any assistance appreciated.

9 - convert to :09
53 - convert to :53
68 - convert to 1:08
109 - convert to 1:49
121 - convert to 2:01
262 - convert to 4:22

This will get it to hours, minutes, and seconds.

=TEXT(ROUNDDOWN(A1/3600,0),"00") & ":" &TEXT(ROUNDDOWN(MOD(A1,3600)/60,0),"00") & ":"&TEXT(MOD(A1,60),"00")

This assumes your list starts in cell A1, then just copy down.

To get rid of leading zeros, you could add an if function, but it becomes complicated:

=IF(A1<60,":"&TEXT(MOD(A1,60),"00"),IF(A1<3600,TEXT(ROUNDDOWN(MOD(A1,3600)/60,0),"00")&":"&TEXT(MOD(A1,60),"00"),TEXT(ROUNDDOWN(A1/3600,0),"00")&":"&TEXT(ROUNDDOWN(MOD(A1,3600)/60,0),"00")&":"&TEXT(MOD(A1,60),"00")))