21990

Appears in sequences

• Number of trees of diameter 7.at n=10A000550
• Number of n-bead necklaces labeled with numbers -1..1 allowing reversal, with sum zero and first and second differences in -1..1.at n=25A208963
• Expansion of chi(q)^5 / chi(q^5) in powers of q where chi() is a Ramanujan theta function.at n=23A225701
• Number of n-node unlabeled rooted trees with thickening limbs and root outdegree (branching factor) 5.at n=40A245145
• a(n) = Sum_{d|n} sigma_3(d).at n=25A321140
• a(n) = Sum_{k=1..n} (-1)^(k+1) * floor((n/k)^3).at n=28A350222
• a(n) is the smallest positive integer which can be represented as the sum of n distinct nonzero tetrahedral numbers in exactly n ways, or -1 if no such integer exists.at n=22A360217
• Triangular array read by rows: T(n,k) = the number of closed meanders with n top arches and k closed meanders in the reduction of the closed meander by the reverse of the exterior arch splitting algorithm.at n=33A363910
• a(n) = Sum_{k=0..floor(n/3)} binomial(n+k-1,k) * binomial(n+k-1,n-3*k).at n=10A389377