RC6 is a fast block cipher. It was developed based on RC5 and does its job quicker than RC5 due to more registers. RC6 uses integer multiplication in its algorithmic computation. RC6 is also rotation-dependent on every word bit, as opposed to the insignificant bits with RC5.
Techopedia explains RC6
RC6 is a derivative of RC5 and is a block cipher designed for RSA Security. RC6 uses four working block size registers in its algorithmic computations, whereas RC5 uses only two. Thus, RC6 is faster. RC6 was designed as part of the Advanced Encryption Standard (AES) competition, where it was a finalist. It is a propriety algorithm patented by RSA Security.