OFFSET
1,1
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
F. Firoozbakht, Puzzle 466. phi(n-1)=phi(n)=phi(n+1), in C. Rivera's Primepuzzles.
MATHEMATICA
Select[Range[7, 60000], EulerPhi[# - 6] == EulerPhi[#] == EulerPhi[# + 6] &] (* T. D. Noe, Sep 24 2012 *)
Flatten[Position[Partition[EulerPhi[Range[60000]], 13, 1], _?(#[[1]] == #[[7]] == #[[13]]&), {1}, Heads->False]]+6 (* Harvey P. Dale, Jun 22 2015 *)
PROG
(PARI) ffd(lim, d=6) = {for (i=1+d, lim-d, m = eulerphi(i); if ((m == eulerphi(i-d)) && (m == eulerphi(i+d)), print1(i, ", "); ); ); }
(PARI) A217006_print(Nmax, d=6)={my(m=2*d+1, o=vector(m, i, eulerphi(if(i>1, i-1, m)))); for(i=m, Nmax+2*d, (o[(i-d)%m+1]==o[i%m+1]=eulerphi(i))||next; o[(i-2*d)%m+1]==o[i%m+1] & print1(i-d", "))} \\ - M. F. Hasler, Sep 23 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Sep 23 2012
STATUS
approved