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 A337640 #15 Sep 17 2020 04:48:20 %S A337640 2,11,35,80,155,266,422,626,890,1223,1625,2108,2678,3341,4109,4988, %T A337640 5990,7106,8348,9734,11264,12953,14801,16820,19019,21389,23957,26717, %U A337640 29663,32834,36230,39860,43712,47795,52139,56726,61598,66746,72152,77837 %N A337640 a(n) = one-half of the number of cells in the central rectangle of the graph described in row 2n+1 of A333288. %C A337640 This is based on _Lars Blomberg_'s data in A333288. %C A337640 A333288 is a triangular array read by rows. a(n) is the central term in row 2n+1 of that triangle, divided by 2. %C A337640 See A331452 for further illustrations. %C A337640 It would be nice to have a formula for this sequence. It is possible that focusing on the points (n, a(n)) where 2n+1 is a prime might lead to a simpler formula. %H A337640 Scott R. Shannon, <a href="/A331452/a331452_6.png">Colored illustration for a(0)</a>: there are 4 regions, so a(0) = 2. %H A337640 Scott R. Shannon, <a href="/A331452/a331452_8.png">Colored illustration for a(1)</a>: the central square has 22 regions, so a(1) = 11. %H A337640 Scott R. Shannon, <a href="/A331452/a331452_10.png">Colored illustration for a(2)</a>: the central square has 70 regions, so a(2) = 35. %H A337640 Scott R. Shannon, <a href="/A331452/a331452_32.png">Colored illustration for a(3)</a>: the central square has 160 regions, so a(3) = 80. %H A337640 Scott R. Shannon, <a href="/A331452/a331452_34.png">Colored illustration for a(4)</a>: the central square has 310 regions, so a(4) = 155. %Y A337640 Cf. A306302, A331452, A333288. %K A337640 nonn %O A337640 0,1 %A A337640 _N. J. A. Sloane_, Sep 17 2020