463061domain: NAppears in sequencesa(0) = 1; a(n) = Sum_{k=0..floor((n-1)/2)} 2^k * a(k) * a(n-2*k-1).at n=18A352006Coefficients in the even function A(x) = Sum_{n>=0} a(n)*x^(2*n) such that: 2 = Sum_{n=-oo..+oo} x^n * (x^n + i*sqrt(A(x)))^n, where i^2 = -1.at n=15A355867