

A167768


First of 4 or more consecutive integers with equal values of phi(phi(n)).


2




OFFSET

1,2


COMMENTS

Next term > 1266046940 (last term of A167767 bfile).  Michel Marcus, Jun 23 2013
No other terms < 1.32*10^12.  Jud McCranie, Jul 19 2017


LINKS

Table of n, a(n) for n=1..7.


EXAMPLE

p2(1) = p2(2) = p2(3) = p2(4) = 1, p2(7) = p2(8) = p2(9) = p2(10) = 2.


MATHEMATICA

a[n_] := EulerPhi[EulerPhi[n]]; Select[Range[10000], a[#] == a[# + 1] && a[# + 1] == a[# + 2] && a[# + 2] == a[# + 3] &] (* G. C. Greubel, Jun 23 2016 *)


PROG

(PARI) pp(n) = eulerphi(eulerphi(n))
isA167768(n) = pp(n)==pp(n+1) && pp(n+1)==pp(n+2) && pp(n+2)==pp(n+3) \\ Michael B. Porter, Nov 24 2009


CROSSREFS

Cf. A167767 (of which this list is a subset), A167766.
Sequence in context: A065916 A122654 A184121 * A103630 A205711 A040064
Adjacent sequences: A167765 A167766 A167767 * A167769 A167770 A167771


KEYWORD

more,nonn,hard


AUTHOR

Fred Schneider, Nov 11 2009


EXTENSIONS

Edited by N. J. A. Sloane, Nov 12 2009
a(7) added by Jud McCranie, Jul 17 2017


STATUS

approved



