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 A217791 Numbers n such that sigma(n) = 3*sigma(n+1). 3
 180, 12000, 30996, 47940, 66780, 102816, 128040, 234300, 494088, 712272, 1133088, 1408212, 1623072, 1692768, 1896336, 1925196, 2024760, 2388720, 2529090, 2836008, 3423120, 3724320, 3822360, 4628760, 4750920, 7219608, 7359912, 7603488, 7749060 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Donovan Johnson, Table of n, a(n) for n = 1..500 EXAMPLE 47940 is in the sequence because sigma(47940)=145152, sigma(47941)=48384, and 145152=3*48384. 7749060 is in the sequence because sigma(7749060)=24192000, sigma(7749061)=8064000, and 24192000=3*8064000. MAPLE A217791:=proc(q) local n; for n from 1 to q do if sigma(n)=3*sigma(n+1) then print(n); fi; od; end: A217791(10^10); MATHEMATICA Position[Partition[DivisorSigma[1, Range[78*10^5]], 2, 1], _?(#[[1]] == 3#[[2]]&), {1}, Heads->False]//Flatten (* Harvey P. Dale, Oct 17 2016 *) PROG (MAGMA) [n: n in [1..10^7] | SumOfDivisors(n) eq 3*SumOfDivisors(n+1)]; // Bruno Berselli, Mar 25 2013 CROSSREFS Cf. A000203, A002961, A058073, A067081, A077087, A163193, A272027 (3*sigma(n)). Sequence in context: A008378 A214818 A287022 * A035830 A244056 A091033 Adjacent sequences:  A217788 A217789 A217790 * A217792 A217793 A217794 KEYWORD nonn AUTHOR Paolo P. Lava, Mar 25 2013 EXTENSIONS More terms from Bruno Berselli, Mar 25 2013 STATUS approved

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Last modified August 10 06:08 EDT 2022. Contains 356029 sequences. (Running on oeis4.)