The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A266005 Numbers n = p_1^s_1...p_m^s_m such that (p_i^s_i - 1) | n for all 0
 1, 2, 6, 12, 42, 60, 84, 156, 168, 240, 420, 504, 660, 720, 780, 840, 1092, 1200, 1404, 1680, 1806, 1860, 2184, 2436, 2520, 2640, 3120, 3600, 3612, 3660, 4032, 4080, 4200, 4620, 4872, 5040, 5460, 6480, 6552, 7020, 7224, 7440, 7920, 8268, 8400, 8580, 9240, 9360, 9576, 9828, 9840, 10920, 11760, 12180, 12240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Robert Israel, Jan 06 2016: (Start) All terms except 1 and 2 are divisible by 6. The only squarefree terms are 1, 2, 6, 42, 1806. (End) LINKS Robert Israel, Table of n, a(n) for n = 1..4000 EXAMPLE 60 is a term since 60 = 2^2*3*5 and is divisible by 2^2-1, 3-1 and 5-1. MAPLE filter:= proc(n) local t; for t in ifactors(n)[2] do if n mod (t[1]^t[2]-1) <> 0 then return false fi od; true end proc: select(filter, [\$1..10^5]); # Robert Israel, Jan 06 2016 MATHEMATICA fa=FactorInteger; G[n_] := Union@Table[IntegerQ[n/(fa[n][[i, 1]]^fa[n][[i, 2]] - 1)], {i, Length[fa[n]]}] === {True}; Select[Range[20000], G] PROG (PARI) isok(n) = {my(f = factor(n)); for (k=1, #f~, if ((n % (f[k, 1]^f[k, 2]-1)), return (0)); ); return (1); } \\ Michel Marcus, Jan 04 2016 CROSSREFS Sequence in context: A080497 A127724 A178008 * A056744 A344184 A164859 Adjacent sequences: A266002 A266003 A266004 * A266006 A266007 A266008 KEYWORD nonn AUTHOR José María Grau Ribas, Dec 20 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 21 15:47 EDT 2024. Contains 372738 sequences. (Running on oeis4.)