The Avestan word hapta
Word hapta
Meaning seven, 7
See also Homeric Greek: ἑπτά ‘seven’
Proto-Indo-European: *septḿ̥ ‘seven’
Armenian: ewtᶜn ‘seven’
Tocharian B: ṣukt ‘seven’
C. Luwian: ša-ap-ta-mi ‘seven’
Mitanni: satta ‘seven’
Hittite: ša-ap-ta ‘seven’
Proto-Celtic: *sextam ‘seven’

Other words that might be of interest
aēuua ‘one’, ašta ‘eight, 8’, xšuuaš ‘six, 6’, θritiia- ‘third’, paoiriia- ‘first’, paṇca ‘five, 5’, bitiia- ‘second’, caθβarasca ‘four’