editing
approved
The e.g.f. can be derived from the functions described by A326797, A326798, and A326799.
Cf. A326797, A326798, A326799.
(PARI)
(PARI) {a(n) = my(C=1, S=x); for(i=1, 2*n+1, ,
S = intformal( C/x * intformal( C +x*O(x^(2*n+1)) ) );
C = 1 - intformal( S/x * intformal( C +x*O(x^(2*n+1)) ) ); ); (2*n+1)!^2*polcoeff(S, C, 2*n+1)}
Cf. A326552, A325291, A326556 (C^2).
The e.g.f. can be derived from the functions described by A326800, A326801, and A326802.
Cf. A326800, A326801, A326802.
also, S(x*y) = sin( Integral Integral C(x*y) dx dy ).,
such that C(x)^2 + S(x)^2 = 1.