A067798 Numbers n such that phi(n)+phi(n+1)=n+1.
1, 2, 3, 5, 9, 15, 21, 35, 39, 45, 75, 99, 135, 231, 255, 363, 483, 765, 855, 1295, 1599, 2015, 2115, 4335, 6783, 9999, 14399, 16095, 16599, 18495, 30495, 53823, 62799, 63455, 65535, 77615, 155319, 186999, 196095, 327675, 589815, 686735, 722015
Offset: 1
Keywords
Links
- Giovanni Resta, Table of n, a(n) for n = 1..76
Programs
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Mathematica
Select[Range[10^5], Plus @@ EulerPhi[{#, # + 1}] == # + 1 &] (* Giovanni Resta, May 15 2016 *) -
PARI
isok(n) = eulerphi(n)+eulerphi(n+1) == n+1; \\ Michel Marcus, May 15 2016
Formula
Extensions
More terms from Dean Hickerson, Feb 16 2002