RosettaCodeData/Task/Yellowstone-sequence/XPL0/yellowstone-sequence.xpl0

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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
]