136990

Appears in sequences

• Sum of numbers that can be written as t*n + u*(n+1) for nonnegative integers t,u in exactly one way.at n=18A076454
• Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.at n=4A163124
• T(n,k) = Number of idempotent n X n 0..k matrices of rank 2.at n=25A224114
• Number of idempotent 5X5 0..n matrices of rank 2.at n=2A224116
• Expansion of (1+4*x+x^2)/((1+x)^2*(1-x)^5).at n=36A233329