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 1-4 of 4 results.

A384838 Numbers k for which sigma(k - x) + sigma(k + x) = 5*k has at least one nonnegative solution.

Original entry on oeis.org

24, 53, 56, 63, 66, 74, 75, 79, 82, 84, 95, 112, 168, 192, 216, 227, 245, 252, 255, 274, 280, 282, 288, 308, 312, 347, 348, 351, 360, 365, 392, 395, 408, 420, 431, 432, 434, 458, 465, 466, 471, 476, 496, 528, 532, 560, 576, 579, 588, 624, 628, 644, 670, 694, 716, 720, 784
Offset: 1

Views

Author

Michel Marcus, Jun 10 2025

Keywords

Links

Crossrefs

Cf. A000203 (sigma), A141643 (a subsequence).
Cf. A383268, A384839, A384840, A384841.
Cf. A383758.

Programs

  • PARI
    isok(k) = for (x=0, k-1, if (sigma(k - x) + sigma(k + x) == 5*k, return(1)));

A384839 Numbers k for which sigma(k - x) + sigma(k + x) = 6*k has at least one nonnegative solution.

Original entry on oeis.org

93, 120, 204, 211, 231, 239, 254, 269, 274, 280, 315, 336, 343, 360, 366, 372, 375, 378, 395, 396, 402, 420, 466, 475, 496, 592, 604, 672, 708, 724, 726, 774, 821, 822, 827, 836, 840, 844, 845, 862, 870, 880, 898, 919, 926, 952, 964, 976, 982, 996, 997, 1023, 1077, 1080
Offset: 1

Views

Author

Michel Marcus, Jun 10 2025

Keywords

Links

Crossrefs

Cf. A000203 (sigma), A005820 (a subsequence).
Cf. A383268, A384838, A384840, A384841.
Cf. A383758.

Programs

  • Mathematica
    s={};Do[Do[If[DivisorSigma[1,k-x]+DivisorSigma[1,k+x]==6*k,AppendTo[s,k];Break[]],{x,0,k-1}],{k,1,1080}];s (* James C. McMahon, Jun 20 2025 *)
  • PARI
    isok(k) = for (x=0, k-1, if (sigma(k - x) + sigma(k + x) == 6*k, return(1)));

A384841 Numbers k for which sigma(k - x) + sigma(k + x) = 8*k has at least one nonnegative solution.

Original entry on oeis.org

14412, 17640, 25581, 25623, 25659, 26208, 30240, 31110, 31380, 31500, 32340, 32736, 32760, 34958, 35112, 44211, 44343, 45048, 45324, 45444, 46578, 48090, 49368, 51674, 52045, 52290, 53103, 53127, 53460, 54000, 54180, 59400, 59940, 60228, 60903, 60914, 60987, 61920, 62340, 62370
Offset: 1

Views

Author

Michel Marcus, Jun 10 2025

Keywords

Links

Crossrefs

Cf. A000203 (sigma), A027687 (a subsequence).
Cf. A383268, A384838, A384839, A384840.
Cf. A383758.

Programs

  • PARI
    isok(k) = for (x=0, k-1, if (sigma(k - x) + sigma(k + x) == 8*k, return(1)));

A385075 Numbers k for which sigma(k - x) + sigma(k + x) = 9*k has at least one nonnegative solution.

Original entry on oeis.org

361881, 792960, 835072, 837312, 846720, 917280, 944608, 946176, 1509236, 1517264, 1630880, 1635600, 1636614, 1697560, 1834560, 1914092, 1926336, 1927692, 1941264, 2387120, 2450112, 2474316, 2494464, 2546656, 2573088, 2624832, 2685394, 2705680, 2840468, 2913120, 2941009
Offset: 1

Views

Author

Michel Marcus, Jun 16 2025

Keywords

Comments

At least one of sigma(k - x) >= 4.5*(k - x) or sigma(k+x) >= 4.5*(k + x) is true. - David A. Corneth, Jun 16 2025

Examples

			361881 is in the sequence via k = 361881 and x = 358839 so k-x = 3042, k+x = 720720 and sigma(k - x) + sigma(k + x) = 7137 + 3249792 = 3256929 = 9*361881 = 9*k. - _David A. Corneth_, Jun 16 2025

Links

Crossrefs

Cf. A000203, A141645 (a subsequence).
Cf. A383268, A384838, A384839, A384840, A384841.
Cf. A383758.

Programs

  • PARI
    isok(k) = forstep(x=k-1, 0, -1, if (sigma(k - x) + sigma(k + x) == 9*k, return(1)));

Extensions

More terms from David A. Corneth, Jun 16 2025
Showing 1-4 of 4 results.

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

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