DB<8> $_ = "105 106 107 108 109 110 111 112 113 213 214";

  DB<9> s[\s?(\d+)\d\d\K\s(?=(\d+)\d\d\s?)]{$1 + 1 == $2 ? "\n" : ' '}ge;

  DB<10> x $_
0  '105 106 107 108 109 110 111 112 113
213 214'
  DB<11>