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 A053098 When the Euler phi function is iterated with initial value A002110(n)=primorial, a(n)= first (maximal) power of 2 emerging during iteration. 0
 2, 2, 8, 16, 128, 512, 8192, 16384, 262144, 2097152, 16777216, 67108864, 2147483648, 8589934592, 274877906944, 4398046511104, 70368744177664, 1125899906842624, 18014398509481984, 288230376151711744 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Analogous to A053047 (the same with a similar large initial value, n!). LINKS EXAMPLE n=6, A002110(6)=30030; the corresponding iteration chain is {30030, 5760, 1536, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1}. The first power of 2 is the 4th item after 3 iterations. It is 512, therefore a(6)=512. MATHEMATICA a[n_] := 2^ Max@ IntegerExponent[ FixedPointList[ EulerPhi, Times @@ Prime[Range[n]]], 2]; Array[a, 20] (* Giovanni Resta, May 30 2018 *) CROSSREFS Cf. A000010, A002110. Sequence in context: A085542 A239682 A009725 * A194588 A175395 A169888 Adjacent sequences:  A053095 A053096 A053097 * A053099 A053100 A053101 KEYWORD nonn AUTHOR Labos Elemer, Feb 28 2000 STATUS approved

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Last modified October 19 13:38 EDT 2018. Contains 316361 sequences. (Running on oeis4.)