@article{GDZPPN002478153, title = {The Length of Periodic Continued Fractions.}, journal = {Monatshefte f\"ur Mathematik}, volume = {76}, year = {1972}, pages = {428-435}, zbl = {0245.10005}, url = {http://dml.mathdoc.fr/item/GDZPPN002478153} }
Hirst, K.E. The Length of Periodic Continued Fractions.. Monatshefte für Mathematik, Tome 76 (1972) pp. 428-435. http://gdmltest.u-ga.fr/item/GDZPPN002478153/