This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A329915 #33 Dec 18 2024 22:01:54
%S A329915 91,77,5882353,52631579,4347826087,3448275862069,
%T A329915 2127659574468085106383,20408163265306122449,
%U A329915 1694915254237288135593220339,16393442622950819672131147541,137,13,112359550561797732809,11,10309278350515463917525773195876288659793814433
%N A329915 a(n) is the least M such that A329914(n) * M = 1M1, where 1M1 denotes the concatenation of 1, M and 1.
%C A329915 When M is a q-digit term, then M is a divisor of 10^(q+1) + 1.
%C A329915 For each term k in A329914, there exist a set of numbers M_k which, when 1 is placed at both ends of M_k, the number M_k is multiplied by k. This sequence gives the smallest integer M(k) = M of each set {M_k}.
%C A329915 See A329914 for further information about these numbers.
%D A329915 D. Wells, 112359550561797732809 entry, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1997, p. 196.
%e A329915 A329914(1) = 21 and 21 * 91 = 1[91]1, and there is no integer < 91 that satisfies this relation, so a(1) = 91.
%e A329915 A329914(2) = 23 and 23 * 77 = 1[77]1, and there is no integer < 77 that satisfies this relation, so a(2) = 77.
%e A329915 A329914(5) = 33 and 33 * 4347826087 = 1[4347826087]1, and there is no integer < 4347826087 that satisfies this relation, so a(5) = 4347826087.
%Y A329915 Cf. A000533, A329914 (corresponding numbers k).
%Y A329915 Some corresponding sets {M_k} : A095372 \ {1} = {M_21}, A331630 = {M_23}, A351237 = {M_83}, A351238 = {M_87}, A351239 = {M_101}.
%K A329915 nonn,base,fini,full
%O A329915 1,1
%A A329915 _Bernard Schott_, Nov 24 2019