40947domain: NAppears in sequencesNumber of planar triangular n X n X n nonnegative integer grids with mirror symmetry about one altitude with every similarly oriented 5 X 5 X 5 subtriangle summing to 10.at n=3A154081a(n) = (2n-1)!!*(Sum_{k=1..n}k/(2*k-1)).at n=5A334066