Question

what is a 17 string or mostly a 13 string instrument ?
[it is a japanese tradition

Answer 1

Koto

Koto are roughly 180 centimetres (71 in) in length, and made from Paulownia wood (Paulownia tomentosa, known as kiri). The most common type uses 13 strings strung over movable bridges used for tuning, different pieces possibly requiring different tuning. 17-string koto are also common, and act as bass in ensembles.