An addition-multiplication chain of length $ l $ for a positive integer $ n $ is a monotonic increasing sequence $ 1 = a_0 < a_1 < \ldots < a_l = n $ of positive integers, such that for each $ 1\leq i \leq l, $ we have $ a_i = {a_j} + {a_k} \ \text{or} \ a_i = {a_j} \times {a_k}, $ where $ 0 \leq k \leq j \leq i-1. $ In this paper, we establish upper bounds for each element in any AM-chain based on the number of squaring steps and the distribution of non-squaring steps preceding the given element. Moreover, we get additional upper bounds independent of the distribution of non-squaring steps. These bounds yield a new upper bound for the number of non-squaring steps in any AM-chain. Finally, we determine all AM-chains that include exactly one small step and, as a consequence, compute the shortest lengths $ \ell_{AM}(.) $ of certain integers.
Citation: S. Tarek, Hatem M. Bahig, M. Anwar. Addition-multiplication chains with one small step[J]. AIMS Mathematics, 2026, 11(6): 16235-16263. doi: 10.3934/Math.2026667
An addition-multiplication chain of length $ l $ for a positive integer $ n $ is a monotonic increasing sequence $ 1 = a_0 < a_1 < \ldots < a_l = n $ of positive integers, such that for each $ 1\leq i \leq l, $ we have $ a_i = {a_j} + {a_k} \ \text{or} \ a_i = {a_j} \times {a_k}, $ where $ 0 \leq k \leq j \leq i-1. $ In this paper, we establish upper bounds for each element in any AM-chain based on the number of squaring steps and the distribution of non-squaring steps preceding the given element. Moreover, we get additional upper bounds independent of the distribution of non-squaring steps. These bounds yield a new upper bound for the number of non-squaring steps in any AM-chain. Finally, we determine all AM-chains that include exactly one small step and, as a consequence, compute the shortest lengths $ \ell_{AM}(.) $ of certain integers.
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