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A363689
Number of alternating sign matrices of size n which are indecomposable by direct and skew sums.
0
1, 1, 0, 1, 16, 257, 5636, 187432, 9956054, 867875816, 125861715682, 30575624363575, 12486657463326416, 8588874417105963246, 9960958211434474577452, 19489076635898035234022220, 64349049302453152886635937502, 358611453994361731825817399132622, 3373425033361375072576454177693810076
OFFSET
0,5
FORMULA
G.f.: 2*(2 - 1/ASM(x)) - ASM(x) where ASM(x) is the g.f. of A005130.
EXAMPLE
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]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ludovic Schwob, Jun 15 2023
STATUS
approved