[math-fun] Concatenate sum of neighbouring digits + iterate

Hello Math-Fun, this is perhaps old hat, I don't know... Take an integer "a" like 962 Sum the first pair of digits: 9+6=14 Sum the next pair: 6+2=8 Concatenate the results: 148 Iterate: 148 --> 512 --> 63 --> 9 Take "b" = 999 999 --> 1818 --> 999 Are there many "looping" integers like 999? Best, É.