291060

Appears in sequences

• Triangle read by rows, the Bell transform of n!*binomial(5,n) (without column 0).at n=41A049411
• Smallest x such that sigma(x) = n*phi(x), or -1 if no such x exists.at n=18A055234
• Numbers k such that k | sigma_7(k) - phi(k)^7.at n=29A055701
• Least balanced numbers (A020492): m such that the quotient sigma(m)/phi(m) equals the n-th prime.at n=7A063513
• Number of subgroups of the group GL(2,Z_n) of invertible 2 X 2 matrices mod n (sequence A000252).at n=25A066514
• a(n) = Min{x : sigma(x) = n*phi(x), x is not a prime}, the least nonprime solutions to sigma(x) = n*phi(x); special balanced numbers.at n=18A088830
• Least common multiple of all cycle sizes in range [A014137(n-1)..A014138(n-1)] of permutation A071665/A071666.at n=9A089875
• Triangle T(n,m)=m*n*binomial(m+n,m)^2/(2*(m+n)) read by rows.at n=19A131635
• The matrix product A127773 * A001263 of infinite lower triangular matrices.at n=49A132818
• Products of two or more consecutive numbers that do not have prime gaps in their factorizations.at n=39A137895
• Triangle T(n,k), n>=0, 0<=k<=n, read by rows: T(n,k) = number of simple graphs on n labeled nodes with k edges where each maximally connected subgraph consists of a single node or has a unique cycle of length 3.at n=43A144207
• A partition product of Stirling_2 type [parameter k = 3] with biggest-part statistic (triangle read by rows).at n=25A157403
• Triangular sequence from coefficients of the polynomial recursion: p(x,n)=Sum[Binomial[n, m]*p[x, m]*p[x, n - m - 1], {m, 0, n - 1}].at n=20A157526
• Oblong numbers that are the product of two oblong numbers.at n=28A188660
• Numbers with prime factorization pqr^2s^2t^3.at n=10A190386
• The Wiener index of the ortho-polyphenyl chain with n hexagons (see the Dou et al. and the Deng references).at n=27A216108
• Irregular triangle read by rows: universal linear relationships among polynomial means for even degrees.at n=28A293107
• Triangular array read by row: T(m,n) = number of ways to obtain a single sphere by gluing the (labeled) sides of a (2m+1)-gon and a (2n+1)-gon, m >= n >= 0.at n=19A297897
• Sum of all the parts in the partitions of n into 9 parts.at n=44A326464
• a(n) = Product_{d|n} A019565(phi(d)), where phi is Euler totient function A000010.at n=43A332824