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 A115100 #14 Jan 29 2013 07:57:11 %S A115100 1,20,360,7200,144000,1872000 %N A115100 Mayan calendar periods in days. %C A115100 "Mayan primes" may be defined as these periods plus or minus 1, namely: 2, 19, 359, 143999, 1872001. Note also that 361 = 19^2; 144001 = 11 * 13 * 19 * 53. %C A115100 From the Hermetic Systems" link: "The Mayas used three different calendrical systems (and some variations within the systems). The three systems are known as the tzolkin (the sacred calendar), the haab (the civil calendar) and the long count system. The tzolkin is a cycle of 260 days and the haab is a cycle of 365 days (these cycles are explained in Sections 2 and 3 of this chapter). The tzolkin cycle and the haab cycle were combined to produce a cycle of 18,980 days, known as the calendar round. 18,980 days is a little less than 52 solar years. %C A115100 "Thus the Mayas could not simply use a tzolkin/haab date to identify a day within a period of several hundred years because there would be several days within this period with the same tzolkin/haab date. The Mayas overcame this problem by using a third dating system which enabled them to identify a day uniquely within a period of 1,872,000 days (approximately 5,125.36 solar years). %C A115100 "To do this they used a vigesimal (i.e. based on 20) place-value number system, analogous to our decimal place-value number system. The Mayas used a pure vigesimal system for counting objects but modified this when counting days." %D A115100 Bourgeois, Julia F., The True Calendar-Years of Aztecs and Mayas and the True Mayan Calendar System, Editorial Cultura, Mexico, 1942. %D A115100 Bowditch, C. P., The Numeration, Calendar Systems and Astronomical Knowledge of the Mayas, Cambridge University Press, 1910. %D A115100 Brunhouse, R. L., Sylvanus G. Morley and the World of the Ancient Mayas, University of Oklahoma Press, 1971. %H A115100 Hermetic Systems: <a href="http://www.hermetic.ch/cal_stud/maya/chap1.htm">Maya and European Dates</a>. %H A115100 <a href="/index/Ca#calendar">Index entries for sequences related to calendars</a> %e A115100 1 kin = 1 day. %e A115100 1 uinal = 20 kins = 20 days. %e A115100 1 tun = 18 uinals = 360 days. %e A115100 1 katun = 20 tuns = 7200 days. %e A115100 1 baktun = 20 katuns = 144000 days. %e A115100 13 baktuns = 1 great cycle or Maya era = 1872000 days (approximately 5125.37 solar years). %Y A115100 Cf. A008684, A008685, A011763, A011770, A011771. %Y A115100 Fortnight related: A001356, A051121. %Y A115100 Related to names of months: A031139. %Y A115100 A subsequence of A081244. %K A115100 easy,fini,full,nonn %O A115100 1,2 %A A115100 _Jonathan Vos Post_, Mar 02 2006 %E A115100 Edited by _M. F. Hasler_, Dec 23 2012