Looks like you need a math lesson. You might want to round to the nearest ten thousandth at least to get YOUR math right. Try using 1138x640 and it's ALMOST perfect. About a quarter pixel off.
1.77777777777778 x 640 = 1137.77777777778 (roughly 1138 and only a quarter pixel off perfect)
1.77777777777778 / 1136 = 639 which is an ENTIRE pixel off perfect. 1138 is a MUCH better choice.
You want verification for that? Simply open up any image editing doc like Photoshop and create a 1920x1080 or 1280x720 16:9 image. THEN, resize the image with "constrain proportions" checked, locked, whatever, and make the height 640. You'll see the width automatically goes to 1138. NOT 1136. This is basic algebra 101. 1136 is NOT a perfect 16:9 image by any means.
Hence the wording in the article that it was *almost* exactly the same ratio, and also the pointed out 16:9.01 aspect ratio in the math to which you just responded.