18720

Appears in sequences

• Smallest k such that sigma(x) = k has exactly n solutions.at n=38A007368
• Expansion of exp(sinh(x))*x.at n=10A009224
• Expansion of sin(sin(x))*x.at n=5A009478
• 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 (4,k)-perfect numbers.at n=45A019293
• Theta series of 8-d 5-modular lattice Q_8(1) with det 625 and minimal norm 4.at n=12A028976
• For all n, if d is recursively applied to a(n) exactly 6 times then the fixed point of d-iteration is just reached.at n=27A036458
• Numbers having four 4's in base 8.at n=16A043440
• Number of double-free subsets of {1, 2, ..., n}.at n=17A050291
• Expansion of e.g.f. (1-x^2)/(1-x-2*x^2+x^4).at n=6A052685
• When expressed in base 3 and then interpreted in base 8, is a multiple of the original number.at n=45A062889
• Numbers k that, when expressed in base 5 and then interpreted in base 8, give a multiple of k.at n=37A062930
• a(n) = 12*n*(n-1).at n=40A064200
• Numbers k such that k+1 is composite and divides 3^k-2^k.at n=32A068410
• Product of the smallest prime divisors of composite numbers between successive primes.at n=52A076976
• Numbers k such that the product of Euler phi of the 2 consecutive integers {k,k+1} is a 4th power: if sqrt(sqrt(phi(k)*phi(k+1))) is an integer, then k is here.at n=9A082788
• Sigma unitary-sigma perfect numbers: numbers m which satisfy the following equation for some integer k: sigma(usigma(m)) = k*m where usigma(m) is sum of unitary divisors of m.at n=24A083288
• a(0) = 1, a(n) = 480*sigma(n).at n=18A083728
• Phi(A033631(n)) {phi is the Euler totient function A000010}.at n=11A115620
• a(1)=1. a(n+1) = n!/lcm(a(1),a(2),...,a(n)).at n=13A131120
• A triangle of recursive Fibonacci Lah numbers: f(n) = Fibonacci(n)*f(n - 1), L(n, k) = binomial(n-1, k-1)*(f(n)/f(k)).at n=22A137478