majenko:
0bnnnnnnnn is C/C++Bnnnnnnnn is a set of #defines in hardware/arduino/cores/arduino/binary.h:
#define B0 0
#define B00 0
#define B000 0
#define B0000 0
#define B00000 0
#define B000000 0
#define B0000000 0
#define B00000000 0
#define B1 1
#define B01 1
#define B001 1
...
If you want to be "proper", use 0bnnnnnnnn.
So (as AWOL says) the Arduino "nicety" is actually a kludge that one should probably avoid if one wants to develop good habits to use outside of ArduinoLand(tm). I'll keep my habit of converting "B" to "0b" when cleaning up examples that I'm learning from...
And base 5 is common in counting. I, II, III, IIII,
IIII
Thinking back on it, that is probably where I got it from.
Edit: corrected quote tags... One of the few times I forget to preview my post, and I put a "/" in the wrong place...