The number 20

Established fact In maths and on the calendar

• 20 is composite, divisible by 2, 4, 5, 10.
• Its digits add up to 2.
• 20 is a side of the 20-21-29 right triangle (20² + 21² = 29²).
• The standard genetic code builds every protein from 20 amino acids, spelled out by 61 of the code’s 64 three-letter codons (the other three mean "stop").
• Every month has a 20th, so it comes round twelve times a year.