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 A079486 #21 Aug 28 2025 17:25:30 %S A079486 3,15,103,879,8787,99061,1227369,16409937,233588249,3504149013, %T A079486 54963273921,895797910129,15094359120933,261882874511985, %U A079486 4662472442136561,84940003965749601,1579633610378515989,29927014639635474589,576597813697577550447,11280469732919709557493 %N A079486 Number of different solutions to a variant of the 3-ball tennis ball problem. %C A079486 You're given labeled balls three at time (labeled 1,2,3 then 4,5,6 etc.), choose two balls from those still on hand (including the three you've just been given) and throw the larger out the window onto the front lawn, the smaller onto the back lawn. %C A079486 a(n) is the number of 2 X n matrices of positive integers, with the numbers in each row and column increasing, the numbers in column k less than or equal to 3k and no number used more than once. %H A079486 Kevin Ryde, <a href="/A079486/b079486.txt">Table of n, a(n) for n = 1..325</a> %H A079486 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a079/A079486.java">Java program</a> (github) %H A079486 Kevin Ryde, <a href="/A079486/a079486.gp.txt">PARI/GP Code and Notes</a> %o A079486 (PARI) \\ See links. %Y A079486 Cf. A000108, A001764, A002293, A049235. %K A079486 nonn,changed %O A079486 1,1 %A A079486 _Barry Cipra_, Jan 19 2003 %E A079486 Larger terms through to a(12) computed by Matt Richey. %E A079486 a(13) onwards from _Sean A. Irvine_, Aug 17 2025