OFFSET
1,1
COMMENTS
See A266276(n) = the smallest numbers k such that phi(k) = n * phi(k-1) for n >=1: 2, 3, 7, 1261, 11242771, ...
FORMULA
a(n) = A172314(n) + 1. - Michel Marcus, Jan 27 2016
EXAMPLE
1261 is in the sequence because phi(1261) = 1152 = 4*phi(1260) = 4*288.
MATHEMATICA
Select[Range@10000000, EulerPhi@# == 4 EulerPhi[# - 1] &] (* Vincenzo Librandi, Jan 27 2016 *)
PROG
(Magma) [n: n in [2..10^7] | EulerPhi(n) eq 4*EulerPhi(n-1)]
(PARI) isok(n) = (eulerphi(n) == 4*eulerphi(n-1)); \\ Michel Marcus, Jan 27 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 26 2016
STATUS
approved