With worksheet functions...

A1 = your text string: 23411268 - 23411270
B1 =LEFT(A1,FIND(" ",A1)-1)+0
C1 =MID(A1,FIND("-",A1)+2,LEN(A1))+0

A3 =IF(MAX($A$2:A2)=$C$1,"",MAX($A$2:A2,$B$1-1)+1)
...copy cell A3 down until the values stop appearing.