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 A355550 #9 Jul 07 2022 05:03:22 %S A355550 0,4,16,1300,976,40300,662704,12251200 %N A355550 a(n) is the smallest number k such that k occurs in the Reverse-and-Multiply trajectories of exactly n positive integers less than k. %C A355550 Smallest k such that A355549(k) = n. %o A355550 (PARI) revmult(n) = n*eval(concat(Vecrev(Str(n)))) %o A355550 a355549(n) = my(i=0); for(k=2, n-1, my(x=k); while(x < n, if(x==revmult(x), break, x=revmult(x))); if(x==n, i++)); i %o A355550 a(n) = for(k=0, oo, if(a355549(k)==n, return(k))) %Y A355550 Cf. A355548, A355549. %K A355550 nonn,base,hard,more %O A355550 0,2 %A A355550 _Felix Fröhlich_, Jul 06 2022 %E A355550 a(5)-a(7) from _Jinyuan Wang_, Jul 07 2022