ANSI Common Lisp 2 Syntax 2.4 Standard Macro Characters 2.4.8 Sharpsign
22.214.171.124 Sharpsign B
#Brational reads rational in binary (radix 2). For example,
#B1101 ==13 ;11012 #b101/11 ==5/3
The consequences are undefined if the token immediately following the #B does not have the syntax of a binary (i.e., radix 2) rational.