A363689 - OEIS

%I #13 Jul 24 2023 15:09:40

%S 1,1,0,1,16,257,5636,187432,9956054,867875816,125861715682,

%T 30575624363575,12486657463326416,8588874417105963246,

%U 9960958211434474577452,19489076635898035234022220,64349049302453152886635937502,358611453994361731825817399132622,3373425033361375072576454177693810076

%N Number of alternating sign matrices of size n which are indecomposable by direct and skew sums.

%F G.f.: 2*(2 - 1/ASM(x)) - ASM(x) where ASM(x) is the g.f. of A005130.

%e a(3) = 1 because the only ASM of size 3 indecomposable by direct and skew sums is

%e   [0  1 0]

%e   [1 -1 1]

%e   [0  1 0]

%Y Cf. A005130, A231498, A359856.

%K nonn

%O 0,5

%A _Ludovic Schwob_, Jun 15 2023