1476304896

Appears in sequences

• 3-perfect (triply perfect, tri-perfect, triperfect or sous-double) numbers: numbers such that the sum of the divisors of n is 3n.at n=4A005820
• Multiply-perfect numbers: n divides sigma(n).at n=17A007691
• Erroneous version of A005820.at n=4A039688
• Multiply perfect numbers that are neither harmonic numbers nor arithmetic numbers.at n=2A046987
• Numbers n such that sigma(n) / n is prime.at n=9A065997
• Abundant numbers n such that n = sigma(k) - 2k, where k = sigma(n) - 2n.at n=6A069085
• Numbers k such that sigma(k)/k, sigma_3(k)/k and sigma_5(k)/k are all integers.at n=10A076231
• Numbers k such that sigma(k)/k and sigma_3(k)/k are both integers.at n=13A076233
• Multiply perfect numbers k for which the quotient sigma_7(k)/k = A013955(k)/k is nonintegral.at n=1A088846
• OU-Sigma multiperfect numbers.at n=22A091321
• Admirable numbers that set a new record for largest subtracted divisor.at n=16A109745
• Let S(n)=sigma(|n|)-2*n; sequence gives numbers n such that S(S(S(S(n))))=n. May be called {2,1}-Sociable number of orders 1 or 2 or 4.at n=25A113285
• Let S(n)=sigma(n)/3. Numbers k such that S(S(k))=k, 1/3-sociable number of order 1 or 2.at n=12A113546
• Multiply perfect numbers k such that sigma(k)/k > 2.at n=11A166069
• Bi-unitary multiperfect numbers.at n=28A189000
• Numbers n such that gcd(sigma(n), n) > gcd(sigma(m), m) for all m < n.at n=30A216793
• Numbers k that divide 2*sigma(k).at n=27A246454
• Nonprime numbers k such that k | (sigma(k) - Sum_{j=1..m}{sigma(k) mod d_j}), where d_j is one of the m divisors of k.at n=22A282775
• Multiply-perfect numbers m from A007691 such that m*(m-tau(m))/sigma(m) is not an integer where k-tau(k) is the number of the non-divisors of k (A049820) and sigma(k) is the sum of the divisors of k (A000203).at n=3A325024
• Multi-perfect numbers from A007691 that are not harmonic (A001599).at n=2A325026