Kyūjitai form of 三畳紀 (“the Triassic period”)

Kyūjitai form of 三毛猫 (“calico cat”)

a tridecagon

the Three Character Classic, a Classical Chinese text / a Japanese text in a similar metre, also known as the 本朝三字経 (honchō sanjikyō)

twenty-three; 23

(mahjong) big three dragons: a 役満 (yakuman, “limit”) hand with triplets or quads of each of the 三元牌 (sangenpai, “dragon tiles”)

(mahjong) little three dragons: a 役 (yaku, “hand”) with triplets or quads of two of the 三元牌 (sangenpai, “dragon tiles”), plus a pair of the third; worth 2 翻 (han, “doubles”). Because 2 翻 is added from the 役牌 (yakuhai, “meld of seat/prevailing wind or dragon”) of the two dragons, the total is actually 4 翻.

(mahjong) Generic name of the three dragon tiles: 白 (haku, “white dragon”), 發/𤼵 (hatsu, “green dragon”), and 中 (chun, “red dragon”)

roast sweet potato

thirty-one; 31