Protein sequence space
= Protein sequence space
{title2=$\{1,\ldots,20\}^n$}
For fixed length $n$ and the standard twenty-amino-acid alphabet, there are $20^n$ sequences: each position has twenty choices. This counts possible sequences, not stable <protein folds>; the sequence-to-structure relationship is many-to-one and some sequences do not form a stable folded protein.