Regarding the word כתר, meaning crown, the numerical value of its final letter (200=ר) is 10 times the first letter (כ=20). The middle letter, Tav, refers to a sign (Yechezkel 9:4). Hence, Keter is the sign of Aliyah, of elevation, as 20 rises ten-fold.
The number 20 hints at the size of the lesser Sanhedrin. The sages explain that the size of this Sanhedrin is a priori two Edot, twenty. However, the number must be odd, and thus the size must be at least 21. Further, a reasoning is brought down why 21 is not a good number, and two more are to be added. The final conclusion is that the lesser Sanhedrin must have 23 members.
I think that a principle of prime numbers is involved here, which the sages could not make explicit. If the sages would have been familiar with the notion of prime numbers, they would have said that 20 is not acceptable because it is not a prime number, and thus the lesser Sanhedrin must count 23 members, the first prime above 20. Similary, the size of the great Sanhedrin, which a priori is 70, must be 71, the first prime number above 70.
The gematria of כתר is 20+400+20*10 = 620. If כתר hints at the Sanhedrin, in the above logic it would seem that its gematria should be prime. Let us try to find a gematria that is prime. If the 20 in כתר refers to the lesser Sanhedrin, a deeper gematria for the word כתר is obtained by computing 23+400+23*10=653. Satisfactorily, this is a prime number. The idea stands.
One step further, we can replace 23 by 71, the size of the great Sanhedrin. This gives 71+400+71*10=1181. This is also a prime number. The idea stands stronger. We know have two prime gematriot for כתר.
In the other direction, we can replace 23 by 3, the size of a minimal Beit Din. This gives 3+400+3*10=433. This is also a prime number. Now we have three prime gematriot.
Yet one step further, just as 20 refers to 3, 23 and 71, the factor 10 refers to powers of 10, to 100 and to 1000. And so, we have the non-prime gematriot:
23+400+23*100 = 2723 = 7*389
23+400+23*1000 = 23423 = 59*397
Interestingly, these numbers have two factors only - they are semiprime. Also semiprime are
3+400+3*100 = 703 = 19*37
3+400+3*1000 = 3403 = 41*83
71+400+71*100 = 7571 = 67*113
Finally,
71+400+71*1000 = 71471
is prime. We have arrived at a very deep gematria of כתר, as the 1000 is related to the great Aleph, Aleph Sofit, related to כתר.
Fascinatingly, 71471 is a factor of the numbers 1143536 and 4574144, associated to the Tikkunim of כתר and the final Samech:
1143536 = 16*71471
4574144 = 64*71471
The circle is closed.
I could elaborate on the numerology, but let me just say the bottom line. At Keter, the Hanhaga of Moshe returns. When Sanhedrin was instituted, Moshe had to be convinced by Yitro. What was Moshe's problem? Did he not understand that he could not do all the work by himself, as Yitro pointed out? Moshe's problem was that he was the only one who could judge according to Truth. He could not delegate this. Yitro convinced him that Moshe's level of judgement was not maintainable throughout the generations. There had to be rules for judgement, law, Halacha. Lesser judges than Moshe could judge according to law. At Keter, the circle is closed. Sanhedrin will reach the level of Moshe. Even the lesser Sanhedrin will judge according to Truth.
