A007539 -id:A007539 - cp's OEIS frontend

A107481 Number of different prime factors of the smallest n-perfect number.

1, 2, 3, 4, 7, 11, 19, 38

Offset: 1

Jose Brox (tautocrona(AT)terra.es), May 27 2005

			a(4)=4 because the smallest 4-perfect number factorization is 2^5*3^3*5*7, which has 4 different prime factors.

Achim Flammenkamp, The Multiply Perfect Numbers Page.

Cf. A001221, A007539, A107482.

a(n) = A001221(A007539(n)).

A107482 Number of prime factors of the smallest n-perfect number.

Original entry on oeis.org

1, 2, 5, 10, 17, 31, 71, 137

Offset: 1

Jose Brox (tautocrona(AT)terra.es), May 27 2005

Multiperfect numbers

			a(4)=10 because the smallest 4-perfect number factorization is 2^5*3^3*5*7 which has 10 prime factors.

Achim Flammenkamp, The Multiply Perfect Numbers Page.

Cf. A107481

a(n) = A001222(A007539(n))

A327630 a(n) is the least integer k such that sigma(sigma(k)) >= n*k where sigma is A000203, the sum of divisors.

Original entry on oeis.org

1, 2, 6, 6, 24, 24, 24, 60, 120, 480, 540, 1560, 2520, 10920, 27720, 30240, 191520, 360360, 360360, 3243240, 5765760, 28828800, 109549440, 438197760, 766846080, 3834230400, 9081072000, 32974381440, 147516969600, 880887047040, 2802822422400

Offset: 1

Michel Marcus, Oct 07 2019

From Daniel Suteu, Oct 10 2019: (Start)
a(32) <= 14814918518400,
a(33) <= 64464915715200,
a(34) <= 709114072867200,
a(35) <= 9881550651772800,
a(36) <= 76648784785372800,
a(37) <= 2376112328346556800. (End)

Cf. A000203, A007539, A023199, A098221, A019278.

Cf. A051027, A272930.

a(n) = my(k=1); while (sigma(sigma(k))/k < n, k++); k;

a(23)-a(29) from Giovanni Resta, Oct 07 2019

a(30)-a(31) from Giovanni Resta, Feb 27 2020

cp's OEIS Frontend

A107481 Number of different prime factors of the smallest n-perfect number.

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A107482 Number of prime factors of the smallest n-perfect number.

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A327630 a(n) is the least integer k such that sigma(sigma(k)) >= n*k where sigma is A000203, the sum of divisors.

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