Yellowstone sequence: Difference between revisions

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 The first 30 Yellowstone numbers are:
 [1, 2, 3, 4, 9, 8, 15, 14, 5, 6, 25, 12, 35, 16, 7, 10, 21, 20, 27, 22, 39, 11, 13, 33, 26, 45, 28, 51, 32, 17]
+</pre>
+=={{header|XPL0}}==
+<lang XPL0>func GCD(N, D);         \Return the greatest common divisor of N and D
+int  N, D, R;           \numerator, denominator, remainder
+[if D > N then
+    [R:=D; D:=N; N:=R]; \swap D and N
+while D > 0 do
+    [R:= rem(N/D);
+    N:= D;
+    D:= R;
+    ];
+return N;
+];
+int I, A(30+1), N, T;
+[for I:= 1 to 3 do A(I):= I;                    \givens
+N:= 4;
+repeat  T:= 4;
+        loop    [if GCD(T, A(N-1)) = 1 and      \relatively prime
+                    GCD(T, A(N-2)) # 1 then     \not relatively prime
+                        [loop   [for I:= 1 to N-1 do \test if in sequence
+                                    if T = A(I) then quit;
+                                quit;
+                                ];
+                        if I = N then           \T is not in sequence so
+                            [A(N):= T;          \ add it in
+                            N:= N+1;
+                            quit;
+                            ];
+                        ];
+                T:= T+1;                        \next trial
+                ];
+until   N > 30;
+for N:= 1 to 30 do
+    [IntOut(0, A(N));  ChOut(0, ^ )];
+\\for N:= 1 to 100 do Point(N, A(N));           \plot demonstration
+]</lang>
+{{out}}
+<pre>
+2 3 4 9 8 15 14 5 6 25 12 35 16 7 10 21 20 27 22 39 11 13 33 26 45 28 51 32 17
 </pre>