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 A363689 #13 Jul 24 2023 15:09:40 %S A363689 1,1,0,1,16,257,5636,187432,9956054,867875816,125861715682, %T A363689 30575624363575,12486657463326416,8588874417105963246, %U A363689 9960958211434474577452,19489076635898035234022220,64349049302453152886635937502,358611453994361731825817399132622,3373425033361375072576454177693810076 %N A363689 Number of alternating sign matrices of size n which are indecomposable by direct and skew sums. %F A363689 G.f.: 2*(2 - 1/ASM(x)) - ASM(x) where ASM(x) is the g.f. of A005130. %e A363689 a(3) = 1 because the only ASM of size 3 indecomposable by direct and skew sums is %e A363689 [0 1 0] %e A363689 [1 -1 1] %e A363689 [0 1 0] %Y A363689 Cf. A005130, A231498, A359856. %K A363689 nonn %O A363689 0,5 %A A363689 _Ludovic Schwob_, Jun 15 2023