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%I #16 Aug 18 2023 23:36:30
%S 0,2,2,2,2,-30,-270,-1438,-6142,-7358,272242,4257922,43023682,
%T 311000610,695755890,-27404769758,-664760994302,-9894650252158,
%U -102388542735118,-391004126650558,14167871151044162,484472962695818850,9626237165050052850,131917051968266058722
%N Imaginary parts of the recursive sequence a(n+2) = Sum_{k=0..n} binomial(n,k)*a(k)*a(n+1-k), with a(0)=1, a(1)=2i.
%C Here, i is the imaginary unit. The complex integer sequence c(n) = A289086(n) + i*A289087(n) is one of a family of sequences whose e.g.f.s satisfy the differential equation f''(z) = f'(z)f(z). For more details, see A289064 and A289082.
%H Stanislav Sykora, <a href="/A289087/b289087.txt">Table of n, a(n) for n = 0..200</a>
%H S. Sykora, <a href="http://dx.doi.org/10.3247/SL6Math17.001">Sequences related to the differential equation f'' = af'f</a>, Stan's Library, Vol. VI, Jun 2017.
%F E.g.f.: imag(2*L0*tan(L0*z + L1)), where L0 = sqrt(i-1/4) and L1 = arccos(sqrt(1+i/4)).
%t a[0]=1; a[1]=2I; a[n_]:=a[n]=Sum[Binomial[n - 2, k] a[k] a[n - 1 - k], {k, 0, n - 2}]; Im[Table[a[n], {n, 0, 50}]] (* _Indranil Ghosh_, Jul 20 2017 *)
%o (PARI) c0=1; c1=2*I; nmax = 200;
%o a=vector(nmax+1); a[1]=c0; a[2]=c1;
%o for(m=0, #a-3, a[m+3]=sum(k=0, m, binomial(m, k)*a[k+1]*a[m+2-k]));
%o imag(a)
%Y Cf. A289086 (real part).
%Y Sequences for other starting pairs: A000111 (1,1), A289064 (1,-1), A289065 (2,-1), A289066 (3,1), A289067 (3,-1), A289068 (1,-2), A289069 (3,-2), A289070 (0,3), A289082 and A289083 (1,i), A289084 and A289085 (2,i), A289088 and A289089 (2,2i).
%K sign
%O 0,2
%A _Stanislav Sykora_, Jul 19 2017
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