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 A003271 Smallest number that requires n iterations of the unitary totient function (A047994) to reach 1. (Formerly M0531) 12
 1, 2, 3, 4, 5, 9, 16, 17, 41, 83, 113, 137, 257, 773, 977, 1657, 2048, 2313, 4001, 5725, 7129, 11117, 17279, 19897, 22409, 39283, 43657, 55457, 120677, 308941, 314521, 465089, 564353, 797931, 1110841, 1310443, 1924159, 2535041, 3637637, 6001937, 8319617, 9453569, 10969369 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A049865(a(n)) = n and A049865(m) <> n for m < a(n). [Reinhard Zumkeller, Aug 17 2011] REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Donovan Johnson, Table of n, a(n) for n = 0..66 (terms < 10^10) R. K. Guy, Letter to N. J. A. Sloane, Apr 1975 M. Lal, Iterates of the unitary totient function, Math. Comp., 28 (1974), 301-302. MATHEMATICA uphi[n_ /; n <= 1] = 1; uphi[n_] := uphi[n] = (f = FactorInteger[n]; Times @@ (f[[All, 1]]^f[[All, 2]] - 1)); b[n_] := (k = 0; FixedPoint[(k++; uphi[#])&, n]; k - 1); a[0] = 1; a[n_] := a[n] = For[an = a[n-1], True, an++, If[b[an] == n, Return[an]]]; Table[Print["a(", n, ") = ", a[n]]; a[n], {n, 0, 42}] (* Jean-François Alcover, Oct 05 2017 *) PROG (Haskell) import Data.List (elemIndex) import Data.Maybe (fromJust) a003271 n = a003271_list !! n a003271_list = map ((+ 1) . fromJust . (`elemIndex` a049865_list)) [0..] -- Reinhard Zumkeller, Aug 17 2011 CROSSREFS Cf. A047994, A049865, A225172, A225173. Sequence in context: A068584 A107799 A329049 * A049796 A106165 A305237 Adjacent sequences:  A003268 A003269 A003270 * A003272 A003273 A003274 KEYWORD nonn,nice,easy AUTHOR EXTENSIONS More terms from David W. Wilson STATUS approved

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Last modified December 11 07:47 EST 2019. Contains 329914 sequences. (Running on oeis4.)