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 A248555 #14 Jul 01 2021 19:03:28
%S A248555 132,465,798,101211,131514,161817,192120,222423,252726,283029,313332,
%T A248555 343635,373938,404241,434544,464847,495150,525453,555756,586059,
%U A248555 616362,646665,676968,707271,737574,767877,798180,828483,858786,889089,919392
%N A248555 a(n) is the concatenation of 3n-2, 3n and 3n-1.
%H A248555 Harvey P. Dale, <a href="/A248555/b248555.txt">Table of n, a(n) for n = 1..1000</a>
%p A248555 read("transforms") ;
%p A248555 A248555 := proc(n)
%p A248555 digcatL([3*n-2,3*n,3*n-1]) ;
%p A248555 end proc:
%p A248555 seq(A248555(n),n=1..70) ; # _R. J. Mathar_, Jan 22 2015
%t A248555 FromDigits[Flatten[IntegerDigits/@{#-2,#,#-1}]]&/@(3*Range[40]) (* _Harvey P. Dale_, Jul 01 2021 *)
%K A248555 nonn,base,less
%O A248555 1,1
%A A248555 _Charles Duvall_, Oct 08 2014