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 A167767 First of 3 or more consecutive integers with equal values of phi(phi(n)). 3
 1, 2, 7, 8, 20, 31, 32, 33, 146, 211, 314, 384, 626, 674, 1754, 2694, 2695, 5186, 11714, 12242, 17329, 17613, 19310, 25544, 35774, 36728, 38018, 40227, 42626, 56834, 65731, 91106, 97724, 110971, 117536, 131071, 131072, 155821, 161734, 164174 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Let p2(n) = phi(phi(n)). This list shows numbers n such that p2(n) = p2(n+1) = p2(n+2) = x for some x. Here phi is Euler's totient function. LINKS Donovan Johnson, Table of n, a(n) for n = 1..500 FORMULA {n: A010554(n) = A010554(n+1) = A010554(n+2)}. - R. J. Mathar, Nov 12 2009 EXAMPLE p2(1) = p2(2) = p2(3) = 1, p2(7) = p2(8) = p2(9) = 2. MATHEMATICA Select[Range[100], EulerPhi[EulerPhi[#]] == EulerPhi[EulerPhi[# + 1]] && EulerPhi[EulerPhi[#]] == EulerPhi[EulerPhi[# + 2]] &] (* G. C. Greubel, Jun 23 2016 *) PROG (PARI) isok(n) = (eulerphi(eulerphi(n)) == eulerphi(eulerphi(n+1))) && (eulerphi(eulerphi(n)) == eulerphi(eulerphi(n+2))) \\ Michel Marcus, Jul 12 2013 (MAGMA) [n: n in [1..2*10^5] | EulerPhi(EulerPhi(n)) eq EulerPhi(EulerPhi(n + 1)) and EulerPhi(EulerPhi(n)) eq EulerPhi(EulerPhi(n + 2))]; // Vincenzo Librandi, Jun 24 2016 CROSSREFS Cf. A167768. Sequence in context: A015617 A306903 A026579 * A054601 A279847 A291629 Adjacent sequences:  A167764 A167765 A167766 * A167768 A167769 A167770 KEYWORD nonn AUTHOR Fred Schneider, Nov 11 2009 EXTENSIONS Edited by N. J. A. Sloane, Nov 12 2009 Extended by R. J. Mathar, Nov 12 2009 STATUS approved

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Last modified May 25 19:30 EDT 2020. Contains 334595 sequences. (Running on oeis4.)