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Maybe its a Remez to the 2nd 40 days that Moshe Rabbeinu was in Shomayim after which Hashem proclaimed Salachti Kidvarecha, so its a hint that its a day of Selichah Umechila for all eternity for Klal Yisroel. Yom Kippur is Yom Kippurim the day that is like Purim…

what does the title have to do with the question?

Torah

There are many different forms of calculation used in gematriah. One of the forms of gematria, termed the reduced value system, is based on the decimal system, where every letter of ten and above reduces to one digit, its numerical lowest common denominator. The fact that mathematics itself is based on the decimal system of ten is of course extremely important. The number ten is highly symbolic and significant in Torah and appears in virtually all manifestations of Jewish tradition.

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Im not a baki on Gematriyah, but what I do know is that there are a number of different ways that the kabbalistic traditions have to do gematriyah and any one of those ways are all valid in kabbalah. Is one better than the other? I don’t know, but they are all valid if its a valid form of gematria. But yes it is very common that mem will be 4.

Reduced value (in Hebrew: mispar katan, modulus 9 in mathematical terminology):

Each letter is reduced to a figure of one digit. For example, in this reckoning, alef equals 1, yud equals 10, kuf equals 100) would all have a numerical value of 1; beit equals 2, kaf equals 20, and reish equals 200 would all have a numerical value of 2, and so on. Thus, the letters have only nine equivalents, rather than twenty-two.

from inner dot org