1612800

Appears in sequences

• Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,9)-perfect numbers.at n=5A019286
• Sum of divisors of k such that k and k+1 have the same number and sum of divisors.at n=18A054005
• Least number whose number of divisors is n-th term from A014613 (numbers of form p*q*r*s, products of exactly 4 primes, counted with multiplicity).at n=24A061218
• Triangle T(k,n) by rows: n! * A075499(k,n).at n=32A099394
• Number of transitive PSL_2(ZZ) actions on a finite dotted and labeled set of size n.at n=7A121356
• Triangle read by rows: T(n,k) is the number of permutations of [n] for which k is the maximal number of initial entries whose parities alternate (1 <= k <= n).at n=45A152660
• Number of permutations of [n] for which the first two entries have the same parity (n>=2).at n=8A152661
• Number of spanning trees in G X P_n, where G = {{1, 2}, {1, 3}, {1, 4}, {1, 5}, {2, 3}, {2, 4}}.at n=2A167059
• Table T(n,m) read by rows: the coefficient of [t^n x^m] of 2*n!*(n+2)!*exp(x*t)*( t*(1-exp(t))-exp(t) ) / (1-exp(t) ), 0<=m<=n+1.at n=47A176990
• a(n) = A002952(n) + A002953(n).at n=17A180277
• Smallest number k such that the symmetric representation of sigma(k) has maximum width n for those k whose representation has nondecreasing width up to the diagonal.at n=17A250071
• G.f. A(x) satisfies: (1 + A(x))^A(x) = (1 + x)^x ; this sequence gives the denominators of the coefficients of x^n in g.f. A(x).at n=10A306091
• For those rows n of A249223 which are weakly increasing, let w(n) denote the maximal entry in the row: sequence gives values of n for which w(n) sets a new record.at n=9A340506
• T(n, k) = denominator([x^k] [z^n] ((1 - i*z)/(1 + i*z))^(i*x)*(1 + z^2)^(-3/4)). Denominators of the coefficients of the symmetric Meixner-Pollaczek polynomials P^(3/4)_{n}(x, Pi/2). Triangle read by rows, T(n, k) for 0 <= k <= n.at n=57A344910
• Maximum difficulty level (see A361424 for the definition) for tiling an n X 3 rectangle with a set of integer-sided rectangles, rounded down to the nearest integer.at n=15A361427