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A258378 O.g.f. satisfies A^3(z) = 1/(1 - z)*( BINOMIAL(BINOMIAL(A(z))) )^2. 6

%I

%S 1,5,37,385,5417,99421,2296077,64510617,2142013137,82103710517,

%T 3566271497845,173005328363057,9265752053418233,542783129304580237,

%U 34511577062800532573,2366512551126709790793,174056559606294111346593,13666923859188010833522789,1140970414332381380968275653

%N O.g.f. satisfies A^3(z) = 1/(1 - z)*( BINOMIAL(BINOMIAL(A(z))) )^2.

%C The binomial transform of an o.g.f. A(z) is given by BINOMIAL(A(z)) = 1/(1 - z)*A(z/(1 - z)).

%C For general remarks on a solution to the functional equation A^(N+1)(z) = 1/(1 - z)*(BINOMIAL(BINOMIAL(A(z))) )^N for integer N, and the connection with triangle A145901 see A258377 (case N = 1). This is the case N = 2.

%C From _Peter Bala_, Dec 06 2017: (Start)

%C a(n) appears to be of the form 4*m + 1. Calculation suggests that for k = 1,2,3,..., the sequence a(n) (mod 2^k) is purely periodic with period length a divisor of 2^(k-1). For example, a(n) (mod 8) = (1, 5, 5, 1, 1, 5, 5, 1,...) seems to be purely periodic with period length 4 and a(n) (mod 16) = (1, 5, 5, 1, 9, 13, 13, 9, 1, 5, 5, 1, 9, 13, 13, 9,...) seems to be purely periodic with period length 8 (both checked up to n = 1000). (End)

%H N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>.

%F a(0) = 1 and for n >= 1, a(n) = 1/n*Sum_{i = 0..n-1} R(i+1,2)*a(n-1-i), where R(n,x) denotes the n-th row polynomial of A145901.

%F O.g.f.: A(z) = 1 + 5*z + 37*z^2 + 385*z^3 + 5417*z^4 + ... satisfies A^3(z) = 1/(1 - z)*1/(1 - 2*z)^2*A^2(z/(1 - 2*z)).

%F O.g.f.: A(z) = exp( Sum_{k >= 1} R(k,2)*z^k/k ).

%p #A258378

%p with(combinat):

%p #recursively define the row polynomials R(n,x) of A145901

%p R := proc (n, x) option remember; if n = 0 then 1 else 1 + x*add(binomial(n, i)*2^(n-i)*R(i,x), i = 0..n-1) end if; end proc:

%p #define a family of sequences depending on an integer parameter k

%p a := proc (n, k) option remember; if n = 0 then 1 else 1/n*add(R(i+1,k)*a(n-1-i,k), i = 0..n-1) end if; end proc:

%p # display the case k = 2

%p seq(a(n,2), n = 0..18);

%t R[n_, x_] := R[n, x] = If[n == 0, 1, 1 + x*Sum[Binomial[n, i]*2^(n - i)*R[i, x], {i, 0, n - 1}]];

%t a[n_, k_] := a[n, k] = If[n == 0, 1, 1/n*Sum[R[i + 1, k]*a[n - 1 - i, k], {i, 0, n - 1}]];

%t a[n_] := a[n, 2];

%t a /@ Range[0, 18] (* _Jean-Fran├žois Alcover_, Oct 02 2019 *)

%Y Cf. A019538, A145901, A258377 (N = 1), A258379 (N = 3), A258380 (N = 4), A258381 (N = 5).

%K nonn,easy

%O 0,2

%A _Peter Bala_, May 28 2015

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Last modified June 14 21:27 EDT 2021. Contains 345041 sequences. (Running on oeis4.)