The probability that a letter is the same is 1/26.
The probability that the first three letters are the same is (1/26) * (1/26) * (1/26).
The probability of the same Amanome is 1/365.
Therefore, the probability that the first three letters of the name are the same and the birthday is the same is (1/26) 3 * (1/365).
California has a population of 25 million.
The number of people with the same first three letters and the same birthday is
2500000000 * (1/26) 3 * (1/365) is approximately equal to 4.