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 A067242 Numbers m such that sigma(m+1)+sigma(m-1) = 5*phi(m). 1
 2, 3, 4, 32, 58, 133, 221, 377, 407, 472, 1241, 1978, 7232, 13181, 13952, 15323, 15409, 17362, 22328, 32048, 44215, 46192, 46498, 46975, 49228, 73169, 74498, 128723, 177305, 241828, 244352, 297477, 306835, 417728, 450023, 455555, 484942, 640729, 693259, 707881, 803509 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..41. MATHEMATICA Select[Range[804000], DivisorSigma[1, #+1]+DivisorSigma[1, #-1] == 5*EulerPhi[ #]&] (* Harvey P. Dale, Jun 22 2021 *) PROG (PARI) isok(m) = (m>1) && (sigma(m+1)+sigma(m-1) == 5*eulerphi(m)); \\ Michel Marcus, Feb 17 2021 CROSSREFS Cf. A000010, A000203, A067243. Sequence in context: A076592 A004844 A037324 * A028354 A028355 A074920 Adjacent sequences: A067239 A067240 A067241 * A067243 A067244 A067245 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Feb 20 2002 EXTENSIONS More terms from Michel Marcus, Feb 17 2021 STATUS approved

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Last modified June 20 11:12 EDT 2024. Contains 373527 sequences. (Running on oeis4.)