A method of detecting and outputting tandem repeats in a sequence of symbols comprising a) mapping the symbols to quaternions; b) constructing a Quaternionic Periodicity Transform (QPT); c) computing the QPT of the sequence to determine the tandem repeats of the sequence; d) post-processing of the QPT; e) outputting a list of tandem repeats obtained from step d) to a computer's memory. In embodiments, the sequence of symbols is a sequence of letters representing nucleotides in a DNA or RNA sequence.