The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A275998 Numbers n such that phi(n^2-1) = phi(n^2+1). 0
 3, 27, 267, 8820000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms below 10^8. - Michel Marcus, Aug 17 2016 LINKS EXAMPLE 3 is a term because phi(3^2-1) = phi(3^2+1). MATHEMATICA Select[Range@10000000, EulerPhi@(#^2 - 1) ==  EulerPhi[#^2 + 1] &] (* Vincenzo Librandi, Aug 18 2016 *) PROG (PARI) isok(n) = eulerphi(n^2-1) == eulerphi(n^2+1); \\ Michel Marcus, Aug 16 2016 (MAGMA) [n: n in [2..100000] | EulerPhi(n^2-1) eq EulerPhi(n^2+1)]; // Vincenzo Librandi, Aug 18 2016 CROSSREFS Cf. A000010, A066812. Sequence in context: A279658 A026294 A199688 * A098401 A011544 A127503 Adjacent sequences:  A275995 A275996 A275997 * A275999 A276000 A276001 KEYWORD nonn,more AUTHOR Altug Alkan, Aug 16 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 30 10:27 EDT 2021. Contains 346359 sequences. (Running on oeis4.)