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 A066671 Powers of 2 arising in A066669: a(n) is the largest even divisor of EulerPhi(A066669(n)), which by definition is a power of 2. 3
 2, 2, 2, 4, 2, 2, 4, 2, 2, 4, 4, 4, 4, 4, 8, 4, 8, 8, 4, 4, 8, 2, 2, 4, 8, 4, 8, 8, 4, 2, 16, 4, 4, 8, 8, 8, 8, 8, 2, 8, 8, 8, 8, 8, 4, 2, 32, 8, 16, 16, 4, 2, 8, 16, 16, 8, 8, 2, 32, 16, 16, 8, 8, 4, 16, 4, 16, 16, 4, 8, 32, 16, 8, 16, 16, 2, 2, 16, 4, 8, 16, 4, 8, 2, 16, 8, 32, 4, 64, 32, 32 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE First, 4th and 15th terms in A066669 are 7, 13, 35; phi(7) = 2*3, phi(13) = 4*3, phi(35) = 24 = 8*3; the largest even divisors (powers of 2) are 2, 4, 8; so a(1) = 2, a(4) = 4, a(15) = 8. MATHEMATICA Select[Array[{#1/#2, #2} & @@ {#, 2^IntegerExponent[#, 2]} &@ EulerPhi@ # &, 200], PrimeQ@ First@ # &][[All, -1]] (* Michael De Vlieger, Dec 08 2018 *) PROG (PARI) lista(nn) = {for (n=1, nn, en=eulerphi(n); if (isprime(p=en>>valuation(en, 2)), print1(en/p, ", ")); ); } \\ Michel Marcus, Jan 03 2017 CROSSREFS Cf. A000010, A065966, A066669, A066670, A066672, A066673. Sequence in context: A160691 A049716 A188903 * A159802 A329586 A255336 Adjacent sequences:  A066668 A066669 A066670 * A066672 A066673 A066674 KEYWORD nonn AUTHOR Labos Elemer, Dec 18 2001 STATUS approved

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Last modified January 22 07:39 EST 2020. Contains 331139 sequences. (Running on oeis4.)