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死算与巧算当然要巧算,但不排斥死算,而且一开始往往只有踏实死算才行。第二个数应该是(4+3+9)×13=208;第三个数应该是(2+0+8)×13=130;第四个数是(1+3+0)×13=52;再算第五个数是(5+2)×13=91;至此为止还看不出什么名堂。只好再继续死算下去:(9+1)×13=130,这时我们眼睛一亮:130又出现了!所得的数已有: 439、208、130、52、91、130……即从130开始,将以3的循环周期不断出现130、52和91这三个数。下面用巧算:先扣去前面两项,即把
Of course, it is necessary to calculate the number of deaths and miscalculations, but it does not exclude deaths, and in the beginning, it is often only practical death. The second number should be (4+3+9)×13=208; the third number should be (2+0+8)×13=130; the fourth number is (1+3+0)×13 =52; The fifth number is again (5+2)×13=91; so far there is nothing to be found. We have to continue to count it down: (9+1)×13=130. At this time, our eyes are bright: 130 has appeared again! The resulting numbers are already: 439, 208, 130, 52, 91, 130... At the beginning of 130, three numbers 130, 52 and 91 will continue to appear in a 3-cycle cycle. The following calculations are used: The first two items are deducted, that is,