There are commands to store a number in a register, to insert the number in the buffer in decimal, and to increment it. These commands can be useful in keyboard macros (see Keyboard Macros).
increment-register) behaves differently if r contains text. See Text Registers.
C-x r i is the same command used to insert any other sort of register contents into the buffer. C-x r + with no numeric argument increments the register value by 1; C-x r n with no numeric argument stores zero in the register.