RosettaCodeData/Task/Fibonacci-sequence/PARI-GP/fibonacci-sequence-12.pari

F=[];
fib(n)={
  if(n>#F,
    F=concat(F, vector(n-#F));
    F[n]=fib(n-1)+fib(n-2)
  ,
    if(n<2,
      n
    ,
      if(F[n],F[n],F[n]=fib(n-1)+fib(n-2))
    )
  );
}