A very severe type of penance, which continues for 16 months, in which the total number of fasting days amounts to 13 months and 17 days, and that of days for intake of food amounts to 2 months and 13 days (73 days) only.
guṇaratnasaṃvatsaraṃ tapaḥ, iha ca trayodaśamāsāḥ saptadaśadinādhikāstapaḥkālaḥ, trisaptatiśca dināni pāranakakāla iti.
(Bhaga 2.61 Vṛ)