OFFSET
0,2
COMMENTS
The number of smooth and commutative discrete aggregation functions on the finite chain L_n={0,1,...,n-1,n}, i.e., the number of monotonic increasing binary functions F: L_n^2->L_n such that F(0,0)=0 and F(n,n)=n, F(x,y)=F(y,x) for all x,y in L_n (commutativity), and F(x+1,y)-F(x,y)<=1 and F(y,x+1)-F(y,x)<=1 for all y in L_n and x in L_n\{n} (smooth).
Also, the number of (n+1)X(n+1) integer symmetric matrices (m_{i,j}) such that m_{1,1}=1, m_{n+1,n+1}=n+1, and all rows and columns are (weakly) monotonic without jumps larger than 1.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Marc Munar, Nov 18 2023
EXTENSIONS
a(0) and a(7)-a(9) from Martin Ehrenstein, Dec 01 2023
STATUS
approved