18620

Appears in sequences

• Harmonic or Ore numbers: numbers k such that the harmonic mean of the divisors of k is an integer.at n=13A001599
• Numbers whose divisors' harmonic and arithmetic means are both integers.at n=10A007340
• Harmonic seed numbers.at n=9A035527
• Maximization of sums of cubes of integer differences (b_[ i ]-i)^3 over permutations {b_[ i ], for i-1,2,...,n} on first n integers.at n=26A049031
• (1+e)-harmonic numbers: harmonic mean of (1+e)-divisors is an integer.at n=11A053783
• Number of symmetric types of (3,2n)-hypergraphs under action of complementing group C(3,2).at n=38A055780
• Duplicate of A007340.at n=10A090944
• Harmonic numbers (A001599) which are not perfect (A000396).at n=9A090945
• a(n) = smallest number m such that m*tau(m)/sigma(m) = n, or 0 if no such m exists.at n=13A091911
• Indices m such that A128646(m)-1 is prime, where A128646 = denominator of partial sums of 1/(p(i)-1).at n=44A137689
• Harmonic numbers that are not multiply-perfect.at n=7A140798
• Corresponding values of arithmetic means of divisors of numbers from A007340.at n=25A157848
• Least common multiple of prime(n)-3 and prime(n)+3.at n=43A166011
• Number of ordered triples (w,x,y) with all terms in {1,...,n} and 2w^3>=x^3+y^3.at n=34A211804
• Numbers k for which sigma(k)/k - 4/7 is an integer.at n=1A218411
• Numbers k such that the product of divisors of sigma(k) is divisible by the product of divisors of k.at n=23A219362
• The second crank moment function M_2(n).at n=19A220909
• Expansion of psi(x^4) / chi(-x)^2 in powers of x where psi(), chi() are Ramanujan theta functions.at n=29A260599
• Integers m such that sigma(m)^2 is divisible by m.at n=33A263928
• a(n) = n*(n + 11)*(n + 22)/6.at n=38A264445