OFFSET
1,1
COMMENTS
All terms are even. Does lim_{n->oo} log(a(n))/log(n) exist?
Are all terms except 2 congruent to 4 (mod 6)? - Robert Israel, Feb 27 2018 [a(3710) = 3044760173456 is the next term after 2 that is congruent to 2 (mod 6). - Amiram Eldar, Jul 17 2022]
Includes the Fermat numbers 2^(2^j)+1 for j = 0..5, but no other terms of A019434. - Benoit Cloitre, corrected by Robert Israel, Mar 02 2018
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..5416 (calculated using the b-file at A001274; terms 1..100 from Robert Israel)
Benoit Cloitre, Plot of log(a(n))/log(n+1) for n=1 up to 62
MAPLE
select(t -> numtheory:-phi(t)+ numtheory:-phi(t-1)=numtheory:-phi(2*t), [seq(i, i=2..10^6, 2)]); # Robert Israel, Feb 27 2018
PROG
(PARI) for(n=2, 200000, if(eulerphi(n) + eulerphi(n-1) == eulerphi(2*n), print1(n, ", ")))
(Magma) [n: n in [2..10^6] | EulerPhi(n)+EulerPhi(n-1) eq EulerPhi(2*n)]; // Bruno Berselli, Feb 27 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 27 2018
EXTENSIONS
More terms from Robert Israel, Feb 27 2018
STATUS
approved