Doo-dah is a period-21tagalong for the 2c/7 orthogonalweekenderspaceship, found by John Winston Garth on December 6, 2020. In its simplest phase, the tagalong part consists entirely of two R-pentomino descendants.[1][2] The spaceship was found using a combination of ikpx2 and apgsearch, with partial results from the former being inputted into the latter via ikpx2's "standard input" feature, with the goal of searching higher-period spaceships and puffers. Garth named the tagalong "doo-dah" after a nickname for his grandfather.[3]
A beehive puffer based on this spaceship was found the same day, seemingly independently by iNoMed[4] and GUYTU6J.[5] GUYTU6J also found a block puffer formed by adding a second weekender to the side of the p21 ship.[5] Both of these puffers can be either one- or two-sided. Various glider rakes have also been constructed.[6][7][8] On December 7, GUYTU6J and Aidan F. Pierce found several period-42 doo-dah-based spaceships.[9][10]
Goldtiger997 found that the p21 tagalong could be added to the weekender with six gliders,[11][2] while iNoMed found that each side could be turned into a beehive puffer with two gliders.[12][2] Finally, gooddogtyson and Blinkerspawn found that the p21 ship could be converted both to and from a puffer with just one glider each way, on each side.[13][14]
