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. 2019 Feb 4;7:43. doi: 10.3389/fchem.2019.00043

Table 1.

Number of possible peptide sequences encompassing the chemical space of peptides of a given length (n).

Peptide length (n) Number of peptides in the chemical space (20n) Chemical space limited to cationic (2) and hydrophobic (8) residues ((2+8)n)
2 400 100
3 8,000 1,000
4 160,000 10,000
5 3,200,000 100,000
6 64,000,000 1,000,000
7 1,280,000,000 10,000,000
8 25,600,000,000 100,000,000
9 512,000,000,000 1,000,000,000
10 10,240,000,000,000 10,000,000,000
20 1.05 × 1026 1 × 1020
30 1.07 × 1039 1 × 1030