Could you tell me a little more what the 54.1 and 46 numbers mean. Is this percent shared segments?
I'm not sure what you mean by "n genomes"
Being female, your father would have passed the X chromosome to you and the Y chromosome to your brother. This represents "sex" chromosomes. Females have 2 X chromosomes and males have an X and a Y. Humans have 46 chromosomes (23 pairs). 22 pairs (or 44 chromosomes) are not "sex" chromosomes; one chromosome of each pair of the 22 would have randomly been passed from a parent to a child.
Your genetic report may have included probabilities based of certain sequences (might be so-called markers like "single nucleotide polymorphisms" or others) that represent the likelihood that you share an ancestor with another person. That is something that would come from the lab. Be sure to check with 23andMe. They should have standardized numbers that could help answer this question.
I hope this helps a little