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 A240237 #9 Sep 09 2017 23:24:31
%S A240237 0,1,2,3,4,5,6,7,8,9,101,110,121,132,143,154,165,176,187,198,202,211,
%T A240237 220,231,242,253,264,275,286,297,303,312,321,330,341,352,363,374,385,
%U A240237 396,404,413,422,431,440,451,462,473,484,495,505,514,523,532,541,550,561,572,583,594,606,615
%N A240237 Concatenated digits of pyramidalized numbers: Write the decimal digits of n (a nonnegative integer) and take successive absolute differences ("pyramidalization"), then concatenate, from left to right, all the digits in each level of the pyramid, and finally concatenate those results for all levels, from the base up. The result is a(n).
%C A240237 Through the so-called "pyramidalization" process a given nonnegative integer is decomposed into its digits, which are "reassembled" afterwards by concatenating each level of the pyramid (separately, from left to right) and subsequently concatenating these results, from the base to the top.
%C A240237 The number of digits of the resulting number is the triangular number t(d) where d is the number of digits in the original number n.
%H A240237 Filipi R. de Oliveira, <a href="/A240237/b240237.txt">Table of n, a(n) for n = 0..9999</a>
%F A240237 a(n) = n for 0 <= n <= 9;
%F A240237 a(n) = 10*n + |floor(n/10) - (n mod 10)| for 10 <= n <= 99.
%e A240237 a(1248) = 1248124121:
%e A240237 1 --> 1
%e A240237 1 2 --> 1.2
%e A240237 1 2 4 --> 1.2.4
%e A240237 1 2 4 8 --> 1.2.4.8 -->> 1248.124.12.1 --> 1248124121
%Y A240237 Cf. A227876, which describes the pyramidalization process, and A000217 (triangular numbers). Cf. also A007908.
%K A240237 nonn,base,easy
%O A240237 0,3
%A A240237 _Filipi R. de Oliveira_, Apr 02 2014