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).
Store number into register r (
If r contains a number, increment the number in that register by
number. Note that command C-x r +
increment-register) behaves differently if r contains
text. See Text Registers.
Insert the number from register r into the buffer.
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.