N = N₀ × 2^n (n = number of divisions)
In binary fission (bacteria) and mitosis (eukaryotes), one cell divides into two identical daughter cells. After n divisions: N = N₀ × 2^n. From a single cell, 10 divisions produce 1,024 cells, 20 divisions produce ~1 million, and 47 divisions produce about 10¹⁴ cells (roughly the number in a human body). A fertilized human egg undergoes approximately 47 rounds of division to build an adult. Cell cycle duration varies: bacteria 20 min (E. coli), yeast 90 min, human cells 24 hours. Cancer involves uncontrolled cell division — tumor doubling times range from 30 days (aggressive) to 500+ days (indolent).