options ls=80 mprint mlogic symbolgen spool ;

data yamhead ;
input a ;
cards;
1
10
11
12
14
15
;
run;

data iset (drop= diff asub i) ;
  set yamhead ;
  diff = a - lag1(a) ;
  b = a - diff ;  * ( = lag1(a) );
  k = a ;
  if (diff > 1) then do ;
    asub = a ;
	a = a - diff ; * set a equal to lag1(a);
    do i = 1 to (diff - 1) ;
      a = a + 1 ;
	  output ;
    end;  * end do i ;
	a = asub;
  end; * if diff ;
  output ;
run;
proc print data=iset ; run ;