cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

A354072 Perfect numbers that are the sum of the divisors of some number.

Original entry on oeis.org

6, 28, 496, 33550336, 8589869056, 137438691328, 2305843008139952128, 2658455991569831744654692615953842176, 191561942608236107294793378084303638130997321548169216, 13164036458569648337239753460458722910223472318386943117783728128
Offset: 1

Views

Author

Jaroslav Krizek, May 16 2022

Keywords

Comments

The distinct values of A000203(A146542(n)).
Conjecture: 8128 is the only perfect number that is not in this sequence.

Examples

			The perfect number 28 is in the sequence because 28 = sigma(12).
sigma(727145809044307968) = sigma(1152771972099211264) = 2305843008139952128.

Links

Crossrefs

Intersection of A000396 and A002191.
Cf. A000203, A146542, A354073, A354074.

Programs

  • Magma
    Set(Sort([&+Divisors(m): m in [1..10^7] | &+Divisors(&+Divisors(m)) eq 2 * &+Divisors(m)]))

Extensions

a(8)-a(10) from Amiram Eldar, May 12 2024

A354074 Factorials that are the sum of the divisors of some m.

Original entry on oeis.org

1, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000, 51090942171709440000, 1124000727777607680000
Offset: 1

Views

Author

Jaroslav Krizek, May 16 2022

Keywords

Comments

Sequence of different values of A000203(A245015(n)).
Conjecture: number 2 is the only factorial that is not in this sequence.

Examples

			Number 24 is in the sequence because sigma(14) = sigma(15) = sigma(23) = 24.

Crossrefs

Intersection of A000142 and A002191.
Cf. A000203, A338112, A055486, A055488, A245015, A354072, A354073, A338112.

Extensions

More terms from Jinyuan Wang, May 17 2022
Showing 1-2 of 2 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement.