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 A357515 #4 Oct 02 2022 00:44:15 %S A357515 105263157894736842, %T A357515 100502512562814070351758793969849246231155778894472361809045226130653266331658291457286432160804020 %N A357515 Smallest positive integer that doubles when the n rightmost digits are shifted to the left end. %C A357515 a(n) with n>=3 is too large to be written in data. %C A357515 The following is a method for finding a(n): Let n be the number of digits shifted, and let m be the smallest positive integer such that 10^m = 2 mod 2*10^n-1. We then look for the smallest positive b that is an n+d digit number and satisfies b = c(10^n-2)/(2*10^d-1), where c is a positive integer. Then a(n) = c(10^n-2)/(2*10^d-1)*10^n+c. %e A357515 a(1) = 105263157894736842 because shifting the 1 rightmost digit to the left end gives 210526315789473684 which is double a(1). %Y A357515 Cf. A146088 %K A357515 nonn,base %O A357515 1,1 %A A357515 _Joseph C. Y. Wong_, Oct 01 2022