The first number of a sequence is 2, and the second number is 3. It is known that starting from the second number of this sequence, each number is 1 less than the product of its two adjacent numbers on the left and right. The first 2005 items of this sequence and how much.
一个数列的第一个数是2，第二个数是3，已知这个数列从第二个数开始每个数都比它左右两个相邻数字的乘积少1，这个数列前2005项的和是多少．
<gadget id="calculator">2 + 3 + 2 + 1 + 1</gadget>
<output>9</output>

<gadget id="calculator">2_005 / 5</gadget>
<output>401</output>

<gadget id="calculator">9 * 401</gadget>
<output>3_609</output>

<result>3_609</result>