80666domain: NAppears in sequencesa(n) = (2*n-1)*(13*n^2-13*n+6)/6.at n=26A063493Number of permutations avoiding the patterns {2431, 3421, 4231, 4321, 24513, 42513, 34512, 43512}; number of strong sorting class based on 2431.at n=11A111285Expansion of Sum_{n>=1} q^(n*(n-1)) / (1-q)^n.at n=48A321481