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 A172002 #11 Jul 20 2016 02:53:04
%S A172002 1,2,3,4,8,9,7,10,6,11,5,12,16,17,15,18,14,19,13,20,29,30,28,31,27,32,
%T A172002 26,33,25,34,24,35,23,36,22,37,21,38,47,48,46,49,45,50,44,51,43,52,42,
%U A172002 53,41,54,40,55,39,56,72,73,71,74,70,75,69,76,68,77,67,78,66,79,65,80
%N A172002 A permutation of the natural numbers in groups of 2*k^2, k=1,2,....
%C A172002 The idea is based on the Janet table of the elements (see A138509 and A171710). Arrange the atomic numbers as if the rows of the table were centered. There are two rows with 2 =2*1^2 elements, 2 rows with 8=2*2^2 elements, 2 rows with 18=2*3^2 elements, and this is extended infinitely by adding 2 rows with 2*k^2 elements (see A137583), incrementing k:
%C A172002 ...........................1...2.........................
%C A172002 ...........................3...4.........................
%C A172002 ..................5..6..7..8...9.10.11.12................
%C A172002 .................13.14.15.16..17.18.19.20................
%C A172002 ..21.22.23.24.25.26.27.28.29..30.31.32.33.34.35.36.37.38.
%C A172002 ..39.40.41.42.43.44.45.46.47..48.49.50.51.52.53.54.55.56.
%C A172002 The sequence is obtained by reading the numbers in each of the rows (top-down), starting with the center left column, then the center right column, and then alternating from the left to the right, increasing the distance to the center until all 2*k^2 numbers of the block are exhausted.
%H A172002 Michael De Vlieger, <a href="/A172002/b172002.txt">Table of n, a(n) for n = 1..10680</a> (First 76 rows)
%H A172002 Anonymous, <a href="http://www.webelements.com/nexus/Janet_Periodic_Table">Janet periodic table</a>, Web Elements Chemistry
%H A172002 Anonymous, <a href="http://www.meta-synthesis.com/webbook/35_pt/pt.html">Periodic Table: Formulations</a>, Chemogenesis web book
%H A172002 Albert Tarantola, <a href="http://www.ipgp.fr/~tarantola/Files/Professional/Mendeleev/">PSE of Elements (Janet form)</a>.
%t A172002 Table[(Riffle[Reverse@ #, Length@ # + #] &@ Range[Ceiling[n/2]^2]) + (# + 1) (3 + 2 #^2 + 4 # - 3 (-1)^#)/12 &[n - 1], {n, 7}] // Flatten (* _Michael De Vlieger_, Jul 19 2016, after _Vincenzo Librandi_ at A168380 *)
%K A172002 nonn
%O A172002 1,2
%A A172002 _Paul Curtz_, Jan 22 2010
%E A172002 Edited by _R. J. Mathar_, Mar 02 2010