Who knows one hundred sixty-six?
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The sun is 166 times the size of the earth (plus change). - Rambam, preface to Commentary on the Mishna
The sefer אברהם אנכי - חלק א here says:
Megillas Esther has 166 posukim (according to the ר' אליעזר מגורמיזא - רוקח) like the gematria of יַעְלְזוּ חֲסִידִים בְּכָבוֹד (Tehillim 149:5), and this corresponds to the number of words in parshas וַיָּבֹא עֲמָלֵק Shemos 17:8-16 plus the words in parshas זָכוֹר Devarim 25:17-19.
It also corresponds to the number of words in Hallel Hagadol (Tehillim 136:1-26) which says in verse 24 וַיִּפְרְקֵנוּ מִצָּרֵינוּ (and He saved us from our adversaries) - an allusion to Haman, אִישׁ צַר וְאוֹיֵב (Esther 7:6). And posuk 25 says נֹתֵן לֶחֶם לְכָל-בָּשָׂר (Who gives bread to all flesh) which is an allusion to the festive meal of Purim. This is the explanation of the answer in the gemara Megillah 14a as to why we don't say Hallel on Purim, because קרייתא זו הלילא - "reading it (Megillas Esther) is Hallel, and since it is called Hallel Hagadol (the Great Hallel) it is greater than the Hallel that we say on all the other festivals.
There is a lot of talk about the Christians censoring 166 years of the Jewish calendar. That would mean we only have 63 years left till the year 6000.
And, bitul b'rov is generally accepted as 1/60, which is 1.66% ;) .