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Increasing Self-Described Sequences
Authors:Y.?-F.?S.?Pétermann  author-information"  >  author-information__contact u-icon-before"  >  mailto:Petermann@math.unige.ch"   title="  Petermann@math.unige.ch"   itemprop="  email"   data-track="  click"   data-track-action="  Email author"   data-track-label="  "  >Email author,Jean-Luc?Rémy
Affiliation:(1) Section de Mathématiques, Université de Genève, 2-4, rue du Lièvre,, C.P. 240, 1211 Genève 24, Switzerland;(2) Laboratoire Lorrain de Recherche en Informatique et ses Applications (LORIA), B.P. 239, 54506 Vand"oelig"uvre-lès-Nancy Cedex, France
Abstract:We proceed with our study of increasing self-described sequences F, beginning with 1 and defined by a functional equation$$|F^{ - 1} (m)| = prodnolimits_{0 leq i leq k} {F_i (m)^{a_i } (1 + o(1))} ;(a_i geq 0;{text{and}};F_i ;{text{denoting}};F circ cdots circ F).$$ In [1] we exhibited the simple solution fprime (t)=Ctbeta, for some beta isin(0,1), of the associated functional-differential equation$$f'(t) = prodnolimits_{0 leq i leq k} {f_i (t)^{ - a_i } } ,$$ and we proved that provided beta<2/(2+d(Gamma)), where$$d(Gamma ): = a_1 + cdots + a_k ,$$ we have the asymtotic equivalence F(m)~ Cmbeta.In the present paper we show that this last result is optimal, in the sense that the self-described sequence defined by |F–1(m)|=F(m)2, that is
$$
1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,6,6,6,6,6,6,6,6,6,7, ldots ,
$$
for which the boundary case beta=2/(2+d(Gamma))(=1/2) holds, does not satisfy F(m) ~ Cmbeta. We also show that the m-th term F(m) of a sequence F for which the boundary case holds is nevertheless of asymptotic order mbeta.Then we investigate the behaviour of self-described sequences F when beta lies beyond the boundary case. In [1] we established the estimates$$m^{beta - varepsilon } ll F(m) ll m^{beta + varepsilon } (*)$$ when beta is the unique fixed point of a certain associated function. We were only able to prove in general that the latter holds when beta does not lie beyond the boundary case, however. In the present paper we prove that whenever$$beta leq {1 mathord{left/
 {vphantom {1 {sqrt {1 + d(Gamma )} }}} right.
 kern-nulldelimiterspace} {sqrt {1 + d(Gamma )} }},$$ beta is the unique fixed point of this function, and in addition we obtain estimates more precise than (*). This applies for instance to the sequence defined by$$|F^{ - 1} (m)| = (F circ F)(m),$$ that is
$$
1,2,2,3,3,4,4,5,5,6,6,6,7,7,7,8,8,8,9,9,9,10,10,10,10,11, ldots ..
$$
Keywords:  KeywordHeading"  >AMS Subject Classification: 11B37  11N37  34K25
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