1-based numbering is the computational idea of indexing an ordered data structure (e.g., a string or array) by starting with 1 instead of 0. For example, if $s$ is the string "ACGT", then $s[1]$ is given by the symbol 'A' and $s[2]$ is 'C'.

By default, problems in Rosalind's Bioinformatics Stronghold will use 1-based numbering instead of 0-based numbering, which is used by Python.