一も二も無く[ichimonimonaku] unhesitatingly
一言二言[hitokotofutakoto] a word or two
一石二鳥[issekinichou] killing two birds with one stone
一二に及ばず[ichininioyobazu] right away
一姫二太郎[ichihimenitarou] It's good to have a girl first and then a boy

うり二つ[urifutatsu] as alike as two melons (two peas in a pod)
黄道十二宮[koudoujuunikyuu] twelve signs of the zodiac
二度[futatabi] again
最小二乗法[saishounijouhou] least-squares method
三十二分音符[sanjuunibuonpu] 32nd note

安倍川餅[abekawamochi] rice cakes (mochi) with Kinako
一倍[ichibai] one share
拡張倍精度[kakuchoubaiseido] extended double-precision
五倍[gobai] five times
公倍数[koubaisuu] common multiple

３倍[sanbai] three-fold
十倍[juubai] ten times
人一倍[hitoichibai] more than others
千倍[senbai] thousand-fold
２倍[nibai] double