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 A294184 #19 Feb 26 2020 00:39:52 %S A294184 1,2,2,4,96,1024,2880,81024,770144,6309300,213812336,6395634044, %T A294184 165849732426,8050337724850,255709623233382 %N A294184 a(n) is the number of ways to arrange numbers from 1 to 2*n in a row, starting with 1, such that the sum of every two adjacent numbers is prime, but also considering the ends as adjacent. %C A294184 When the size of the row is odd, it is impossible to find such an arrangement, so that sequence is only defined for even-sized rows. %H A294184 Situ Zhengmei, <a href="https://zhuanlan.zhihu.com/p/85591313">Prime ring</a>, Chinese Math Blog. %F A294184 a(n) = 2*A051252(n), for n > 1. - _Giovanni Resta_, Feb 25 2020 %e A294184 a(1) = 1, because of [1, 2]. %e A294184 a(2) = 2, because of [1, 2, 3, 4] and [1, 4, 3, 2]. %e A294184 a(3) = 2, because of [1, 4, 3, 2, 5, 6] and [1, 6, 5, 2, 3, 4]. %Y A294184 Cf. A036440, A051252, A051239, A242527, A242528. %K A294184 nonn,more %O A294184 1,2 %A A294184 _Michel Marcus_, Feb 11 2018 %E A294184 a(9)-a(11) from _Jackson Bahm_, Feb 25 2020 %E A294184 a(12)-(15) from _Giovanni Resta_, using A051252, Feb 25 2020