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 A320467 #22 Jan 27 2019 09:14:57
%S A320467 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,1,14,2,
%T A320467 15,3,16,4,17,5,18,6,19,7,20,8,1,9,2,10,3,11,4,12,5,13,6,1,7,2,8,3,9,
%U A320467 4,10,5,11,6,12,7,13,8,14,9,15,10,16,11,17,12,18
%N A320467 Two-column table read by rows: The Mayan 260-day Tzolkin cycle, with day names replaced by numbers.
%C A320467 Day 1 of year 1 of the Mayan Long Count calendar (0.0.1.0.1) coincides with the first day of the Tzolkin cycle (1,1). Two Tzolkin cycles before that date, there was a new moon.
%H A320467 Lucian Craciun, <a href="/A320467/b320467.txt">Table of n, a(n) for n = 1..520</a>
%H A320467 John Walker, <a href="http://www.fourmilab.ch/documents/calendar">Calendar Converter</a>.
%H A320467 Wikipedia, <a href="http://en.wikipedia.org/wiki/Tzolk'in">Tzolk'in</a>.
%H A320467 Wikipedia, <a href="http://en.wikipedia.org/wiki/Mesoamerican_Long_Count_calendar">Mesoamerican Long Count calendar</a>.
%F A320467 a(2n-1) = ((n - 1) mod 13) + 1.
%F A320467 a(2n) = ((n - 1) mod 20) + 1.
%F A320467 a(n) = ((n - 1)/2 mod 13 + 1)*(n mod 2) + ((n/2 - 1) mod 20 + 1)*(1 - (n mod 2)). - _Stefano Spezia_, Dec 07 2018
%e A320467 The first pair, (1,1), represents 1 Imix; the second pair, (2,2), represents 2 Ik; the thirteenth pair, (13,13), represents 13 Ben; the fourteenth pair, (1,14), represents 1 Ix; the fifteenth pair, (2,15), represents 2 Men; etc.
%t A320467 For[{A := {}, k := 0}, k < 260, k++, A = Append[A, {1 + Mod[k, 13], 1 + Mod[k, 20]}]]; Flatten[A]
%t A320467 a[n_]:=(Mod[(n-1)/2, 13] + 1)*Mod[n, 2]+(Mod[n/2-1, 20] + 1)*(1-Mod[n, 2]); Array[a, 260] (* _Stefano Spezia_, Dec 07 2018 *)
%Y A320467 Cf. A081244, A215146.
%K A320467 easy,fini,full,nonn,tabf
%O A320467 1,3
%A A320467 _Lucian Craciun_, Oct 13 2018