20080

Appears in sequences

• Numbers n such that n divides the (right) concatenation of all numbers <= n written in base 21 (most significant digit on right).at n=19A029514
• G.f. is ((1-x)/(1-2*x)) * G(x*(1-x)/(1-2*x)) where G(x) is g.f. for Catalan numbers A000108.at n=8A059279
• Numbers k such that phi(k)+sigma(k) is a perfect cube.at n=12A061366
• Numbers m such that phi(m) = tau(m)^3.at n=14A068559
• a(n) = 11 + floor((2 + Sum_{j=1..n-1} a(j))/3).at n=26A120156
• A Moessner triangle using (1, 2, 1, 2, 1, 2, ...).at n=30A125751
• Number of rooted trees with n points and exactly k specified colors: C(n,k), 1<=n, 1<=k<=n.at n=19A141610
• G.f.: 1/(1 + x - x^2 - x^3 + x^4).at n=37A199803
• Trisection 1 of A199803.at n=12A199931
• Numbers with at least three digits and with the property that the sum of the cubes of the first and last digit equals the number obtained when the first and last digits are deleted.at n=34A275343
• Square array A(n,k), n >= 0, k >= 0, read by antidiagonals, where column k is the expansion of e.g.f. 1/(1 + k*log(1 - x)).at n=49A320079
• Triangle read by rows: T(n, k) = qStirling1(n, k, q) for q = 2, with 0 <= k <= n.at n=42A333142
• a(n) = floor(x(n)) where x(n) = (frac(x(n-1))+1)*floor(x(n-1)) and x(1) = Pi.at n=25A339412
• Lesser of a pair of amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A162296(k) - k is the sum of aliquot divisors of k that have a square factor.at n=2A357495
• Expansion of e.g.f. 1 / (1 + 5 * log(1-x)).at n=4A365588