OFFSET
1,1
COMMENTS
Often a(k) == 0 (mod 3) and if a(k+1) - a(k) = 1 then a(k+1) == 0 (mod 3).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[500], ! Divisible[EulerPhi[#*(# + 1)*(# + 2)/6], EulerPhi[#*(# + 1)/2]] &] (* Amiram Eldar, Jul 17 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Jan 28 2002
STATUS
approved