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URL: https://oeis.org/A384839

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A384839
Numbers k for which sigma(k - x) + sigma(k + x) = 6*k has at least one nonnegative solution.
5
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
1,1
LINKS
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 *)
PROG
(PARI) isok(k) = for (x=0, k-1, if (sigma(k - x) + sigma(k + x) == 6*k, return(1)));
CROSSREFS
Cf. A000203 (sigma), A005820 (a subsequence).
Cf. A383758.
Sequence in context: A039550 A167776 A099019 * A082131 A249300 A153684
KEYWORD
nonn
AUTHOR
Michel Marcus, Jun 10 2025
STATUS
approved