Not a sum: the name is counted. It is transmitted as a sequence of forty-two letters, so its value as a number is the count of its letters and not a gematria of the sequence. The form in liturgical use is the acrostic of the forty-two words of Ana BeKhoach.
The forty-two-letter name is the one the Talmud discusses most fully, and it may be transmitted only to one who is discreet, humble, past half his life and slow to anger. Its 42 is also the number of the wilderness stations in Numbers 33, which the tradition reads as the forty-two stages of a life, one letter for each. It is treated as a name of mercy, and the prayer that encodes it is recited before the open ark.
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