Quotes:U

H. P. Blavatsky

U. U — The twenty‐first letter of the Latin alphabet, which has no equivalent in Hebrew. As a number, however, it is considered very mystical both by the Pythagoreans and the Kabbalists, as it is the product of 3 x 7. The latter consider it the most sacred of the odd numbers, as 21 is the sum of the numerical value of the Divine Name aeie, or eiea, or again aheihe — thus (read backward, aheihe) he i he a 5+10+5+1=21 In Alchemy it symbolizes the twenty‐one days necessary for the transmutation of baser metals into silver.

Source: H. P. Blavatsky, The Theosophical Glossary, art. U