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 A289718 #9 Sep 02 2017 16:04:01 %S A289718 1,4,27,180,1015,5028,23051,101272,434835,1843320,7753471,32440884, %T A289718 135195307,561615460,2326740315,9617256944,39671268187,163352387952, %U A289718 671559953015,2756930503420,11303415274179,46290177094172,189368906605747,773942488240920,3160265160762575,12893881856438128,52567364492251191,214163336821005012,871950728486358835,3547937446945462500 %N A289718 The order of the semigroup of orientation-preserving or reserving full transformations of n elements. %H A289718 A. Umar, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Umar/umar2.html">Combinatorial Results for Semigroups of Orientation-Preserving Partial Transformations</a>, J. Int. Seq. 14 (2011) # 11.7.5, corollary 31, table 3.4 and 3.5. %F A289718 a(n) = A005430(n)-n*A006004(n). %p A289718 A289718 := proc(n) %p A289718 n*binomial(2*n,n)-n^2*(n^2-2*n+5)/2+n ; %p A289718 end proc: %K A289718 nonn,easy %O A289718 1,2 %A A289718 _R. J. Mathar_, Sep 02 2017