137638 rounded to the nearest hundred thousand is 100000.
The answer will depend on what you wish to do with the estimated number. If, for example you wanted to multiply by 15.3, then I would suggest 140000. Then 137638*15.3 = approx 140000*15 = 2100000. If, on the other hand, you wanted to subtract 5600 then I would suggest 137600. Then 137638 - 5600 = approx 137600 - 5600 = 13200.
The answer depends on what you wish to do with the estimated number. If dividing by 15 I suggest 135000 because 135000/15 = 9000. If multiplying by 142, then I would suggest 140000, since 137638*142 = approx 140000*140 = 19600000.