2178540

Appears in sequences

• Multiply-perfect numbers: n divides sigma(n).at n=10A007691
• 4-perfect (quadruply-perfect or sous-triple) numbers: sum of divisors of n is 4n.at n=2A027687
• Multiply perfect numbers that are also harmonic numbers but are not arithmetic numbers.at n=3A046986
• Numbers k whose average divisor is nonintegral and divides k.at n=4A046999
• Digitally balanced numbers in base 8: equal numbers of 0's, 1's, ..., 7's.at n=17A049359
• Numbers m such that m = sigma(abs(k)) - 3k, where k = sigma(m) - 3m.at n=6A069146
• Multiply perfect numbers k for which the quotient sigma_3(k)/k = A001158(k)/k is nonintegral.at n=1A088844
• Numbers k that divide (sum of proper divisors of k + product of proper divisors of k).at n=10A089748
• Numbers k such that S(S(k))=k, with S(n)=sigma(n)/4: 1/4-sociable numbers of order 1 or 2.at n=5A113286
• Let S(n)=sigma(|n|)-3*n; sequence gives numbers n such that S(S(S(S(n))))=n. May be called {3,1}-Sociable number of orders 1 or 2 or 4.at n=8A114528
• Let S(n)=sigma(|n|)/2-n; sequence gives numbers n such that S(S(S(S(n))))=n. May be called {1,2}-sociable number of orders 1 or 2 or 4.at n=8A114529
• Multiperfect numbers sigma(n) = k*n, which are divisible by the sum of their prime factors without repetition.at n=3A114887
• Near-multiperfects with primes, powers of 2, 6 * prime and 2^n * prime excluded, abs(sigma(n) mod n) <= log(n).at n=33A117350
• Multiply perfect numbers k such that sigma(k)/k > 2.at n=5A166069
• Largest members of fully k-sociable cycles of order r.at n=33A183023
• Conjectured list of smallest members of fully k-sociable cycles of order r.at n=34A183026
• Numbers with prime factorization pqrs^2t^2u^2.at n=16A190391
• Numbers n such that gcd(sigma(n), n) > gcd(sigma(m), m) for all m < n.at n=19A216793
• Numbers n with the property that, if tau(n) = k = number of divisors of n, and the d(i) are the divisors [arranged in increasing order], then the sum 1/d(k) + 1/d(k-1) + 1/d(k-2) + ... + 1/d(q) is an integer for some q.at n=21A226476
• Numbers n such that Sum_{i = 1..q} 1/d(i) is an integer where d(i) are the divisors of n for some q and n is primitive (the set {d(1), d(2), ..., d(q)} appears only once).at n=30A226853