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 A162923 Numbers n such that the equation sigma(sigma(x)) = n has no solutions. 2
 2, 3, 5, 6, 9, 10, 11, 13, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 33, 34, 35, 36, 37, 38, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 61, 62, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 85, 86, 87, 88, 89, 92, 93 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Ivan Neretin, Table of n, a(n) for n = 1..10000 FORMULA {A000027} minus {A070286}. MATHEMATICA mx = 100; Complement[Range[mx], Table[Nest[DivisorSigma[1, #] &, n, 2], {n, mx}]] (* Ivan Neretin, Feb 12 2018 *) CROSSREFS Complement of A070286. Sequence in context: A230044 A069861 A047449 * A107040 A045989 A129832 Adjacent sequences:  A162920 A162921 A162922 * A162924 A162925 A162926 KEYWORD nonn AUTHOR Jaroslav Krizek, Jul 17 2009 STATUS approved

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Last modified December 14 19:27 EST 2019. Contains 329987 sequences. (Running on oeis4.)