136584

Appears in sequences

• Number of index n subgroups of modular group PSL_2(Z).at n=19A005133
• Triangular array read by rows. T(n,k) is the number of labeled rooted trees of height at most 2 with exactly k leaves at a distance 1 from the root, n>=1, 0<=k<=n-1.at n=37A220233
• Triangle of coefficients T(n,k) of polynomials p(n,x) = Sum_{k=0..n} T(n,k)*x^k where T(0,0) = 1, and T(n,k) = 0 for k < 0 or k > n, and T(n,k) = T(n-1,k-1) + (2*n-1+k)*T(n-1,k) for n > 0 and 0 <= k <= n.at n=51A265649
• a(n) = a(n-1) + 6*a(n-3) + 2*a(n-4), with a(0) = a(1) = 1, a(2) = 3, a(3) = 6.at n=15A339600
• Triangular array T(n,k) read by rows: column k is the expansion of e.g.f: exp(-2*x)*(exp(x)-1)^k/(2-exp(x)).at n=40A372245