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A066812 a(n) is such that phi(a(n)+1) = phi(a(n)-1). 7
5, 8, 9, 11, 27, 33, 71, 75, 123, 147, 309, 315, 387, 513, 555, 573, 627, 636, 729, 795, 843, 911, 915, 1016, 1083, 1227, 1323, 1331, 1347, 1467, 1515, 1609, 1755, 1995, 2133, 2171, 2187, 2307, 2403, 2427, 2475, 2591, 2643, 2696, 2763, 2907, 3243, 3315 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) is even for n=2,18,24,44,67 while a(n) is odd for other values of n < 85.

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000

FORMULA

Conjecture: there is a constant 2 < c < 2.1 such that a(n)=n^c asymptotically.

MATHEMATICA

Flatten[Position[Partition[EulerPhi[Range[3400]], 3, 1], _?(#[[1]]== #[[3]]&), 1, Heads->False]]+1 (* Harvey P. Dale, Apr 18 2018 *)

PROG

(PARI) { n=0; a=1; for (m=1, 10^10, while (1, a++; if (eulerphi(a+1) == eulerphi(a-1), break)); write("b066812.txt", n++, " ", a); if (n==1000, return) ) } \\ Harry J. Smith, Mar 29 2010

CROSSREFS

A001494(n) + 1.

Sequence in context: A314571 A191977 A101079 * A100832 A314572 A034812

Adjacent sequences:  A066809 A066810 A066811 * A066813 A066814 A066815

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jan 20 2002

EXTENSIONS

Corrected by Ralf Stephan, Feb 20 2004

STATUS

approved

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Last modified May 19 10:55 EDT 2019. Contains 323390 sequences. (Running on oeis4.)