A363689 Number of alternating sign matrices of size n which are indecomposable by direct and skew sums.
1, 1, 0, 1, 16, 257, 5636, 187432, 9956054, 867875816, 125861715682, 30575624363575, 12486657463326416, 8588874417105963246, 9960958211434474577452, 19489076635898035234022220, 64349049302453152886635937502, 358611453994361731825817399132622, 3373425033361375072576454177693810076
Offset: 0
Keywords
Examples
a(3) = 1 because the only ASM of size 3 indecomposable by direct and skew sums is [0 1 0] [1 -1 1] [0 1 0]
Formula
G.f.: 2*(2 - 1/ASM(x)) - ASM(x) where ASM(x) is the g.f. of A005130.