79982domain: NAppears in sequencesa(n) = floor((Pi/2)^n).at n=25A014214Let M = 2 X 2 matrix [ 1 2 / 5 4 ]; a(n) = (1,2) entry of M^n.at n=6A092165Number of odd amicable pairs where the smaller term of the pair is less than 10^n.at n=15A360054