335780006100domain: NAppears in sequencesa(n) = (2n+1)!/n!^2.at n=18A002457First numerator and then denominator of central elements of Leibniz's Harmonic Triangle.at n=37A046212a(0) = 1; for n >= 1, a(n) = A059897(n, a(n-1)).at n=37A284567