Hofstadter Q sequence: Difference between revisions

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 Q(9) = 6
 Q(10) = 6
+Q(1000) = 502</pre>
+=={{header|COBOL}}==
+<lang cobol>        IDENTIFICATION DIVISION.
+        PROGRAM-ID. Q-SEQ.
+        DATA DIVISION.
+        WORKING-STORAGE SECTION.
+SEQ.
+Q         PIC 9(3) OCCURS 1000 TIMES.
+Q-TMP1    PIC 9(3).
+Q-TMP2    PIC 9(3).
+N         PIC 9(4).
+DISPLAYING.
+ITEM      PIC Z(3).
+IX        PIC Z(4).
+        PROCEDURE DIVISION.
+        MAIN-PROGRAM.
+            PERFORM GENERATE-SEQUENCE.
+            PERFORM SHOW-ITEM
+                VARYING N FROM 1 BY 1
+                UNTIL N IS GREATER THAN 10.
+            SET N TO 1000.
+            PERFORM SHOW-ITEM.
+            STOP RUN.
+        GENERATE-SEQUENCE.
+            SET Q(1) TO 1.
+            SET Q(2) TO 1.
+            PERFORM GENERATE-ITEM
+                VARYING N FROM 3 BY 1
+                UNTIL N IS GREATER THAN 1000.
+        GENERATE-ITEM.
+            COMPUTE Q-TMP1 = N - Q(N - 1).
+            COMPUTE Q-TMP2 = N - Q(N - 2).
+            COMPUTE Q(N) = Q(Q-TMP1) + Q(Q-TMP2).
+        SHOW-ITEM.
+            MOVE N TO IX.
+            MOVE Q(N) TO ITEM.
+            DISPLAY 'Q(' IX ') = ' ITEM.</lang>
+{{out}}
+<pre>Q(   1) =   1
+Q(   2) =   1
+Q(   3) =   2
+Q(   4) =   3
+Q(   5) =   3
+Q(   6) =   4
+Q(   7) =   5
+Q(   8) =   5
+Q(   9) =   6
+Q(  10) =   6
 Q(1000) = 502</pre>