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 A383429 #12 May 05 2025 00:26:02 %S A383429 1,11,112,1123,11234,112345,1123456,11234567,112345678,1123456789, %T A383429 112345678910,11234567891012,1123456789101214,112345678910121416, %U A383429 11234567891012141618,1123456789101214161820,112345678910121416182022,11234567891012141618202224 %N A383429 a(1)=1, and for n>1, a(n) = a(n-1) concatenated with the length of the decimal representation of a(n-1). %H A383429 Jason Bard, <a href="/A383429/b383429.txt">Table of n, a(n) for n = 1..355</a> %e A383429 a(5) = 11234 and A055642(a(5)) = 5, so a(6) = 112345. %t A383429 A[n_]:=NestList[#<>ToString[StringLength[#]]&,"1",n-1]; A[355] %o A383429 (PARI) lista(nn) = my(va=vector(nn)); va[1] = 1; for (n=2, nn, va[n] = fromdigits(concat(digits(va[n-1]), digits(#Str(va[n-1]))));); va; \\ _Michel Marcus_, Apr 30 2025 %Y A383429 Cf. A007908, A055642, A117804. %K A383429 nonn,base,easy %O A383429 1,2 %A A383429 _Jason Bard_, Apr 27 2025