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.

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A291373 a(n) is the smallest number k such that A001065(k) = A002110(n), or 0 if no such k exists.

Original entry on oeis.org

2, 0, 6, 841, 0, 1722, 30018, 0
Offset: 0

Views

Author

Altug Alkan, Aug 23 2017

Keywords

Comments

a(10) = 4057230930. - Giovanni Resta, Aug 23 2017

Examples

			a(5) = 1722 because sigma(1722) - 1722 = 2*3*5*7*11 = A002110(5) and 1722 is the least number with this property.

Crossrefs

Cf. A001065, A002110, A070015, A153076, A291356.

Formula

a(n) = A070015(A002110(n)). - Michel Marcus, Aug 25 2017

Extensions

a(7) confirmed by Giovanni Resta, Aug 23 2017

A362440 Aliqout sequence starting at 841.

Original entry on oeis.org

841, 30, 42, 54, 66, 78, 90, 144, 259, 45, 33, 15, 9, 4, 3, 1, 0
Offset: 1

Views

Author

N. J. A. Sloane, Apr 22 2023

Keywords

Comments

This is 841 followed by A008885. Could be further extended backwards, see A070015.

References

  • GCHQ, The GCHQ Puzzle Book, Penguin, 2016. See page 92.

Crossrefs

Cf. A001065, A008885, A070015.

Programs

  • Mathematica
    NestWhileList[DivisorSigma[1,#]-#&,841,#>0&] (* Paolo Xausa, Oct 16 2023 *)
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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