300865domain: NAppears in sequencesNumber of n X 2 binary arrays with each 1 adjacent to exactly one 0 vertically and one 0 horizontally.at n=19A183344One of the two successive approximations up to 13^n for 13-adic integer sqrt(-3). Here the 6 (mod 13) case (except for n = 0).at n=5A322089