Formula of Love: O+T=<3 is TWICE's 3rd Korean studio album, released November 12, 2021 via JYP Entertainment and Republic Records. The physical release originally came in four versions — Study About Love, Break It, Explosion, and Full of Love — with a fifth version, Result File, added December 17 following the album's success. Each version includes a photobook, CD, Index Photo Paper (1 of 9), Scientist ID Card (2 of 18), DIY sticker, Break Scratch Card (1 of 10), and 4 photocards (4 of 60); pre-orders added a full photocard set and folded poster per version. The album's concept frames TWICE as scientists at a "Love Lab," with the title spelling out "Once + Twice = Love" — O and T being fandom and group initials, while the <3 also marks this as their third studio entry. The 16-track disco-pop and synth-pop album features TWICE's first English single "The Feels" (pre-released October 1), lead single "Scientist," all-English tracks "Moonlight," "Icon," and fan dedication "Candy," plus three unit tracks — "Push&Pull" (Jihyo, Sana, Dahyun), "Hello" (Nayeon, Momo, Chaeyoung), and "1,3,2" (Jeongyeon, Mina, Tzuyu). Members Nayeon, Jihyo, Dahyun, and Chaeyoung received songwriting credits. The album surpassed 700,000 pre-order sales before release, debuted at #3 on the Billboard 200, and was certified KMCA 3× Platinum — TWICE's first triple platinum certification. A monograph followed on March 16, 2022.