619642domain: NAppears in sequencesApproximation of the 2-adic integer arctanh(2) up to 2^n.at n=20A309753Approximation of the 2-adic integer arctanh(2) up to 2^n.at n=21A309753Approximation of the 2-adic integer arctanh(2) up to 2^n.at n=22A309753a(n) is the number of free polyominoes of width 3 and size n.at n=14A353067