62762119216domain: NAppears in sequencesMaximal term in Collatz-iteration started at -1+2^n.at n=21A087701a(n) = 2*(3^n - 1).at n=22A100774Number of palindromes (in base 9) below 9^n.at n=21A117868a(n) is the last number in the (2n+1)-element alternating sequence of x/2 and (3x+1) iterations starting with A277215(n).at n=22A277874