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

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..76

Formula

{n: A000010(n) = A051953(n+1)}. - Omar E. Pol, May 15 2016

Mathematica

Select[Range[10^5], Plus @@ EulerPhi[{#, # + 1}] == # + 1 &] (* Giovanni Resta, May 15 2016 *)

Prog

(PARI) isok(n) = eulerphi(n)+eulerphi(n+1) == n+1; \\ Michel Marcus, May 15 2016

Crossrefs

Cf. A000010, A051953, A067796.

Sequence in context: A085897 A361906 A306829 * A205536 A281704 A350607

Adjacent sequences: A067795 A067796 A067797 * A067799 A067800 A067801

Keyword

nonn

Author

Benoit Cloitre, Feb 07 2002

Extensions

More terms from Dean Hickerson, Feb 16 2002

Status

approved