Meaning of B111?

freqError = static_cast<int32_t>(readRegister(REG_FREQ_ERROR_MSB) & B111);

I want the above C++ code to convert it to C.
But what is this 'B111'?
What 's it 's equivalent in C?

0b111, or 0x07, or 07, or just 7

Oh, it's binary b00000111.
Thank you!
I got confused because it had only 3 digits.

From the Arduino core file binary.h

#define B111 7