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A217006
Numbers n such that phi(n-6) = phi(n) = phi(n+6).
2
78, 84, 222, 228, 438, 738, 948, 1158, 3252, 5058, 5268, 6918, 7212, 7362, 8082, 8292, 9732, 12108, 13842, 14562, 15348, 15558, 15858, 17148, 17502, 18372, 22482, 23202, 26148, 26652, 30468, 33492, 34212, 38028, 39828, 39972, 41988, 44508, 49332, 54738, 55092
OFFSET
1,1
LINKS
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
Sequence in context: A181467 A344812 A345476 * A053083 A246487 A039435
KEYWORD
nonn
AUTHOR
Michel Marcus, Sep 23 2012
STATUS
approved