      SUBROUTINE ISBIT(N,I) 
*-----------------------------------------------------------------------
*   
*   Sets the bit I ( 0 < I < 26)  in word N , rightmost = 1 .   
*   Bits can be tested with ITBIT.  
*   
*-----------------------------------------------------------------------
      DIMENSION NP(26)  
      SAVE IFIRST
      DATA IFIRST/0/
      IF(IFIRST.EQ.0)  THEN 
         IFIRST=1   
         NP(1)=1
         DO 10 J=2,26   
            NP(J)=2*NP(J-1) 
   10    CONTINUE   
      ENDIF 
      IF(I.GT.0.AND.I.LE.25)  THEN  
         IF (ITBIT(N,I).EQ.0) N=N+NP(I) 
      ENDIF 
      END   
