201812domain: NAppears in sequencesa(n) = 6^n-5^n+1^n.at n=7A155639Number of permutations of length n which avoid the patterns 321 and 1324.at n=30A179257Expansion of x^3*(1-2x-x^2-x^3+x^4+x^5)/((1+x)*(1-3x+x^2-x^3+3x^4)).at n=19A248091