51001180160
domain: N
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=5A005820
- Multiply-perfect numbers: n divides sigma(n).at n=22A007691
- 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 (2,12)-perfect numbers.at n=11A019289
- Multiply perfect numbers whose average divisor is an integer and divides the number itself.at n=8A046985
- Numbers n such that sigma(n) / n is prime.at n=13A065997
- Abundant numbers n such that n = sigma(k) - 2k, where k = sigma(n) - 2n.at n=7A069085
- Numbers k such that sigma(k)/k, sigma_3(k)/k and sigma_5(k)/k are all integers.at n=13A076231
- Numbers k such that sigma(k)/k and sigma_3(k)/k are both integers.at n=16A076233
- Numbers k such that sigma(k)/k, sigma_3(k)/k, sigma_5(k)/k and sigma_7(k)/k are all integers.at n=11A076234
- Admirable numbers that set a new record for largest subtracted divisor.at n=19A109745
- 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=13A113546
- Multiply perfect numbers k such that sigma(k)/k > 2.at n=15A166069
- 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=27A282775
- Numbers m such that lcm(tau(m), m) = sigma(m) where sigma(k) = the sum of the divisors of k (A000203) and tau(k) = the number of the divisors of k (A000005).at n=3A306667
- Multiperfect numbers m such that sigma(m) is also multiperfect.at n=2A323653
- 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=5A325024
- Numbers that are multi-perfect (A007691) and simultaneously harmonic (A001599).at n=18A325025
- Multiply-perfect numbers (A007691) that are arithmetic (A003601).at n=8A331724
- Numbers m such that g(m) = (m * tau(m) / sigma(m)), h(m) = (m * sigma(m)) / tau(m) and k(m) = (tau(m) * sigma(m)) / m are all integers.at n=16A333639
- Numbers m such that the sum of the first k divisors of m, for some k, is equal to the sum of its other divisors.at n=19A334410