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 A271983 The smaller of a pair n, m such that phi(n) = phi(m) and there is no other k such that phi(n) = phi(k). 0
 1, 11, 23, 29, 31, 47, 53, 81, 59, 67, 71, 79, 83, 103, 107, 121, 127, 131, 137, 139, 149, 151, 167, 173, 179, 191, 197, 199, 211, 223, 227, 229, 239, 251, 263, 269, 271, 283, 293, 343, 307, 311, 317, 331, 361, 347, 359, 367, 373, 379, 383, 389, 419, 431, 439, 443, 463, 467, 479, 491, 499 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If phi(x) = N has exactly two solutions, x = n and x = m, say (see A007366), it is conjectured that one of n and m is odd and the other even. This sequence differs from A058340 in that it contains nonprime integers.  The first few are 81, 121, 343, 361, 529, 649, 841, 961, 1219, 1331, 1537, 1633, ... LINKS EXAMPLE 81 is a term because phi(81) = phi(162) = 54 (= A007366(8)). MATHEMATICA (* takes about 2 minutes, can return the sequence up to terms less than 5760=Euler phi(13 primorial) *) Prepend[Select[    Table[Flatten[Position[Table[EulerPhi[n], {n, 1, 30030}], m]], {m,      2, 500, 2}], Length[#] == 2 &][[All, 1]], 1] CROSSREFS Cf. A007366, A058340. Sequence in context: A086102 A058340 A138537 * A136000 A054723 A109981 Adjacent sequences:  A271980 A271981 A271982 * A271984 A271985 A271986 KEYWORD nonn AUTHOR Geoffrey Critzer, Apr 17 2016 EXTENSIONS Edited by N. J. A. Sloane, Apr 22 2016 at the suggestion of Franklin T. Adams-Watters. STATUS approved

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Last modified December 5 12:24 EST 2021. Contains 349557 sequences. (Running on oeis4.)