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Iterated cyclic exponentials and power functions with extra-periodic first coefficients
A. P. Bulanov Obninsk State Technical University for Nuclear Power Engineering
Abstract:
If $f$ is the iterated $m$-cyclic exponential
$$
f(z)=e^{\lambda\alpha_1ze^{\alpha_2ze^{\dots}}}=
\langle e^z;\lambda\alpha_1,\alpha_2,\dots,\alpha_m,\alpha_1,\dots\rangle,
$$
where the first coefficient, $\lambda\alpha_1$, in the sequence of coefficients is extra-periodic,
then in its power series expansion at $z=0$, $\sum_{n=0}^\infty\frac1{n!}H^{(n)}(f) z^n$,
the form $H^{(n)}(f)$ can be written as
\begin{align*}
H^{(n)}(f)
&=\lambda\alpha_1\sum_{k_1+\dots+k_m=n}\frac{n!}{k_1!\dotsb k_m!}
(k_1\alpha_2)^{k_2}(k_2\alpha_3)^{k_3}
\\
&\qquad\times\dots\times(k_{m-1}\alpha_m)^{k_m}[(k_m+\lambda)\alpha_1]^{k_1-1}.
\end{align*}
This formula is generalized to any number of extra-periodic coefficients at the start of the sequence.
It is also shown that in some cases iterated cyclic exponentials whose first coefficients are not elements of the $m$-cyclic sequence $(\alpha_1,\alpha_2,\dots,\alpha_m,\alpha_1,\dots)$ can furnish a solution of a first-order system of differential equations with rational right-hand side.
Bibliography: 32 titles.
Keywords:
iterated exponential, cyclic exponential, iterated power function, cyclic power function, coefficient of an exponential, sequence.
Received: 23.07.2008 and 15.07.2009
Citation:
A. P. Bulanov, “Iterated cyclic exponentials and power functions with extra-periodic first coefficients”, Sb. Math., 201:1 (2010), 23–55
Linking options:
https://www.mathnet.ru/eng/sm6395https://doi.org/10.1070/SM2010v201n01ABEH004064 https://www.mathnet.ru/eng/sm/v201/i1/p25
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Abstract page: | 948 | Russian version PDF: | 636 | English version PDF: | 21 | References: | 90 | First page: | 22 |
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