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 A231811 Numbers n such that p-1 divides n+1 for every prime divisor p of n. 2
 1, 2, 3, 4, 8, 9, 15, 16, 27, 32, 35, 64, 75, 81, 99, 128, 135, 243, 255, 256, 375, 455, 512, 539, 675, 729, 783, 875, 1024, 1089, 1215, 1295, 1715, 1859, 1875, 2048, 2115, 2187, 2375, 2703, 2975, 3375, 3519, 4096, 4335, 4355, 5375, 5915, 6075, 6479, 6561, 6723 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers of the form 2^k, k >= 0, and 3*5^m, m >= 0, are terms. - Marius A. Burtea, Oct 02 2019 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 MATHEMATICA fa = FactorInteger; Gu[n_] := Union@Table[IntegerQ[(n + 1)/(fa[n][[i, 1]] - 1)], {i, Length[fa[n]]}]; Select[Range[20000], Gu[#] == {True} &] PROG (PARI) isok(n) = {my(f=factor(n)[, 1]); for (k=1, #f~, if ((n+1) % (f[k]-1), return(0)); ); return(1); } \\ Michel Marcus, Oct 02 2019 (Magma) [1] cat [k: k in [2..7000]| #[p:p in PrimeDivisors(k)| IsIntegral((k+1)/(p-1))] eq #PrimeDivisors(k)]; // Marius A. Burtea, Oct 02 2019 CROSSREFS Cf. A231810. Sequence in context: A057844 A281089 A242333 * A015922 A373725 A212255 Adjacent sequences: A231808 A231809 A231810 * A231812 A231813 A231814 KEYWORD nonn AUTHOR José María Grau Ribas, Jan 20 2014 EXTENSIONS Term 1 prepended by Max Alekseyev, Jan 20 2014 STATUS approved

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Last modified September 19 09:52 EDT 2024. Contains 376008 sequences. (Running on oeis4.)