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 A091289 Integer solutions x to sigma(x) + sigma(x+1) = 2*sigma(2x+1) where sigma = A000203. 2
 215, 923, 944, 1715, 2379, 5355, 38429, 87584, 110483, 212795, 291039, 1016519, 1051644, 1198139, 2729979, 9380447, 9397674, 31476500, 31749948, 33146259, 33497064, 47004099, 50482278, 52026408, 54114528, 61571795, 79000679, 162914079, 190974539, 212196564, 277017455 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..31. MATHEMATICA Do[s=(DivisorSigma[1, n]+DivisorSigma[1, n+1])/ DivisorSigma[1, 2*n+1]; If[Equal[s, 2], Print[n]], {n, 1, 10000000}] PROG (PARI) isok(n) = sigma(n) + sigma(n+1) == 2*sigma(2*n+1); \\ Michel Marcus, Jul 29 2017 CROSSREFS Cf. A000203, A091287, A067171, A091290. Sequence in context: A259889 A362201 A137205 * A085754 A232252 A002239 Adjacent sequences: A091286 A091287 A091288 * A091290 A091291 A091292 KEYWORD nonn AUTHOR Labos Elemer, Feb 16 2004 EXTENSIONS a(16)-a(27) from Donovan Johnson, Jan 31 2009 a(28)-a(31) from Amiram Eldar, May 23 2022 STATUS approved

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Last modified August 12 10:21 EDT 2024. Contains 375092 sequences. (Running on oeis4.)