There is a class of natural numbers, starting from the third number, each number is exactly the sum of the two numbers before it, until it can no longer be written, such as 257, 1459, etc. How many such numbers are there?
有一类自然数，从第三个数字开始，每个数字都恰好是它前面两个数字之和，直至不能再写为止，如257、1459等等，这类数共有多少个．
<gadget id="calculator">1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9</gadget>
<output>45</output>

<result>45</result>