91392

Appears in sequences

• A unitary phi reciprocal amicable number: consider two different numbers r, s which satisfy the following equation for some integer k: uphi(r) = uphi(s) = (1/k) * r * s / (r-s); or equivalently, 1/uphi(r) = 1/uphi(s) = k * (1/s - 1/r); sequence gives r numbers.at n=20A080766
• Triangle read by rows: T(n,k), n >=1, 0 <= k <= C(n,k), = number of n X n symmetric positive semi-definite matrices with 2's on the main diagonal and 1's and 0's elsewhere and with k 1's above the diagonal.at n=68A083029
• Number of (directed) Hamiltonian paths (or Gray codes) on the n-cube.at n=3A091299
• a(n) = 2^n * binomial(3n,n)/(2n+1).at n=6A153231
• Triangle T(n,m) read by rows: let p(n,x) = exp(-x) * Sum_{m >= 0} (2*m + 1)^n * x^m/m!; then T(n,m) = [x^m] p(n,x).at n=42A154537
• The fourth row of the ED2 array A167560.at n=27A167561
• Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 diagonally or antidiagonally neighboring 1.at n=5A191551
• Number of directed Hamiltonian paths on the n X n torus grid graph.at n=1A276291
• Triangle read by rows: T(n,k) (n >= 1, 1 <= k <= n) = number of normalized 2n-plets associated to trees with k edges.at n=42A294439
• a(n) = (2*n + 4)!*(n^2 + 11*n + 2)/(2*(n-1)!*(n+6)!).at n=6A294445
• a(n) = (6*n)!/((3*n)!*(2*n)!) * (3*n/2)!/(5*n/2)!.at n=3A347857
• Number of permutations of 0..n-1 which are binary Gray codes.at n=15A385185