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.

A066590 Numbers which can be expressed as product of a number and its reversal in at least three different ways.

Original entry on oeis.org

635040, 1015560, 1446480, 1854720, 4356000, 6350400, 10155600, 14464800, 18547200, 43560000, 51665040, 59552640, 63504000, 67944240, 76839840, 78127560, 82623060, 88560360, 95236960, 99497160, 101556000, 105094080
Offset: 1

Views

Author

Robert G. Wilson v, Jan 08 2002

Keywords

Comments

A066598 is a subsequence, e.g., a(2)=A066598(1). - M. F. Hasler, Feb 14 2012

Examples

			63540 = 1440 * 411 = 2520 * 252 = 4410 * 144.

Links

Crossrefs

Cf. A066531, A066598.

Programs

  • Mathematica
    f[n_] := (m = ToExpression[StringReverse[ToString[n]]]; If[n > m, n*m, 0]); a = Sort[ Table[ f[n], {n, 0, 10^6}]]; While[ a[[1]] == 0, a = Drop[a, 1]]; a[[ Select[ Range[ Length[a]] - 2, a[[ # ]] == a[[ # + 2 ]] & ]]]

Extensions

Definition clarified by M. F. Hasler, Feb 14 2012
Definition corrected by N. J. A. Sloane, Aug 01 2019

A386221 Numbers which can be expressed as the product of a number and its binary reversal in at least three different ways.

Original entry on oeis.org

2371610879733375, 8379443074856875, 103889625367330285, 162508095102648823, 2143169709271976875, 2481725627762299375, 4055619414785589625, 8167773178498814075, 9027536760163222895, 133527604616779133915, 133893081609954481115, 137216105281788994475, 457495296809227508125
Offset: 1

Views

Author

Zhao Hui Du, Aug 12 2025

Keywords

Comments

It appears that most numbers that can be expressed in three different ways can also be expressed in four different ways. For a(n) < 2^88, only 11 numbers can be expressed in exactly three ways while 691 numbers can be expressed in exactly four ways.

Examples

			2371610879733375 = 51606261*45955875 = 64244529*36915375 = 64338225*36861615 while 51606261 = 11000100110111001011110101_2, 45955875 = 10101111010011101100100011_2 and reverse(11000100110111001011110101) = 10101111010011101100100011.
8379443074856875 = 101377465*82655875 = 102886105*81443875 = 114021425*73490075 = 115718225*72412475.

Links

Crossrefs

Cf. A066531, A066598.
Showing 1-2 of 2 results.

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

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