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 A038395 #33 Feb 17 2024 10:30:52
%S A038395 1,31,531,7531,97531,1197531,131197531,15131197531,1715131197531,
%T A038395 191715131197531,21191715131197531,2321191715131197531,
%U A038395 252321191715131197531,27252321191715131197531,2927252321191715131197531,312927252321191715131197531
%N A038395 Concatenation of the first n odd numbers in reverse order.
%C A038395 a(n) starts with the digits of 2n-1. Indices of prime or probable prime terms are 1,2,37,62,409,...: see also A089922. - _M. F. Hasler_, Apr 13 2008
%C A038395 If n == 0 (mod 3), so is a(n). - _Sergey Pavlov_, Mar 29 2017
%D A038395 Mihaly Bencze [Beneze] and L. Tutescu, Some Notions and Questions in Number Theory, Sequence 3.
%H A038395 Florentin Smarandache, <a href="http://arXiv.org/abs/math/0604019">Sequences of Numbers Involved in Unsolved Problems</a>, arXiv:math/0604019 [math.GM], 2006.
%t A038395 Table[FromDigits[Flatten[IntegerDigits/@Join[Reverse[Range[1,n,2]]]]], {n,1,29,2}] (* _Harvey P. Dale_, Jun 02 2011 *)
%o A038395 (PARI) t=""; for( n=1,10^3, ( t=eval( Str( 2*n-1,t))) & print(n" "t)) \\ _M. F. Hasler_, Apr 13 2008
%o A038395 (Python)
%o A038395 def a(n): return int("".join(map(str, range(2*n-1, 0, -2))))
%o A038395 print([a(n) for n in range(1, 17)]) # _Michael S. Branicky_, Jan 31 2021
%Y A038395 Cf. A089922, A109837, A038394-A038399, A019518, A019519.
%K A038395 nonn,base,easy
%O A038395 1,2
%A A038395 M. I. Petrescu (mipetrescu(AT)yahoo.com)
%E A038395 Edited and extended by _M. F. Hasler_, Apr 13 2008
%E A038395 Edited by _T. D. Noe_, Oct 30 2008