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 A305785 #6 Jun 10 2018 13:32:15 %S A305785 1,1,1,2,3,7,14,33,84,204,627,1558,5692,14402,60752,155828,747046, %T A305785 1937292,10385051,27176489,161160411,424958631,2760858706,7327447983, %U A305785 51762453941,138150105263,1054164297384,2827224795106,23174732414244,62420125297576,546984814641114 %N A305785 Number of set partitions of [n] with alternating parity of elements and exactly ceiling(n/2) blocks. %H A305785 Wikipedia, <a href="https://en.wikipedia.org/wiki/Partition_of_a_set">Partition of a set</a> %F A305785 a(n) = A274581(n,ceiling(n/2)). %e A305785 a(5) = 7: 123|4|5, 12|34|5, 12|3|45, 1|234|5, 145|2|3, 1|2|345, 1|23|45. %Y A305785 Cf. A274581. %K A305785 nonn %O A305785 0,4 %A A305785 _Alois P. Heinz_, Jun 10 2018