I always write a simple mysql application that does a "select to_days(now()) - to_days('certain special date')" using bind vars if the language supports it -- which they all should by now I hope.

I then write a Fibonacci generator as close to this recursive formula as possible (ignoring the fact that there are better ways to do it):

use strict;

for my $i (0 .. 35) {
    print "i=$i ... fib(i)=", fib($i), "\n";
}

sub fib {
    my $n = shift;

    return fib($n-1) + fib($n-2) if $n>1;
    return 1;
}
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