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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A331099 The numbers such that the sum of their proper divisors plus the product of their digits equals the number.

Original entry on oeis.org

1, 14, 27, 154, 284, 574, 1264, 2588, 7288, 49852, 2342656, 33550336, 8589869056
Offset: 1

Views

Author

Scott R. Shannon, Jan 09 2020

Keywords

Comments

The perfect numbers containing a 0 digit are all in this sequence.
a(14) > 10^13. - Giovanni Resta, Jan 19 2020

Examples

			14 is a term as A001065(14) = 10, A007954(14) = 4, and 10 + 4 = 14.
2588 is a term as A001065(2588) = 1948, A007954(2588) = 640, and 1948 + 640 = 2588.

Crossrefs

Cf. A001065, A007954, A331098.

Programs

  • Magma
    [k:k in [1..2500000]| k eq &*Intseq(k)+DivisorSigma(1,k)-k]; // Marius A. Burtea, Jan 18 2020
  • Mathematica
    Select[Range[10^6], DivisorSigma[1, #] + Times @@ IntegerDigits[#] == 2 # &] (* Amiram Eldar, Jan 18 2020 *)
  • PARI
    isok(n) = my(d=digits(n)); sigma(n) + vecprod(d) == 2*n; \\ Jinyuan Wang, Jan 19 2020

Extensions

a(12) from Jinyuan Wang, Jan 19 2020
a(13) from Giovanni Resta, Jan 19 2020
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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