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 A068666 #16 Mar 03 2024 21:06:57
%S A068666 5,55,5005,55055,50155105,5065665605,50155155155105,
%T A068666 5464353998993534645,541025148469303964841520145,
%U A068666 513016415223221833242338122322514610315
%N A068666 a(1) = 5; a(n) = smallest palindromic multiple of a(n-1).
%t A068666 a[1] = 5; a[n_] := a[n] = Block[{k = 2}, While[k*a[n - 1] != ToExpression[ StringReverse[ ToString[k*a[n - 1]]]], k++ ]; k*a[n - 1]]; Table[a[n], {n, 1, 9}]
%t A068666 spm[n_]:=Module[{k=2},While[!PalindromeQ[k*n],k++];k*n]; NestList[spm,5,10] (* _Harvey P. Dale_, Nov 10 2022 *)
%Y A068666 Cf. A068664, A068665, A068667, A068668, A070069, A068971, A068972, A068973, A068974.
%K A068666 base,nonn,more
%O A068666 1,1
%A A068666 _Amarnath Murthy_, Mar 01 2002
%E A068666 Corrected and extended by _David W. Wilson_ and _Patrick De Geest_, Mar 30 2002
%E A068666 a(10) from _John Gustaf Stebbins_, Sep 17 2008