OFFSET
1,1
COMMENTS
Pollack (2011) proved that the complementary sequence has asymptotic density 7/8. Therefore the asymptotic density of this sequence is 1/8.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Paul Pollack, Values of the Euler and Carmichael functions which are sums of three squares, Integers, Vol. 11 (2011), pp. 145-161.
EXAMPLE
1 is not a term since phi(1) = 1 = 0^2 + 0^2 + 1^2 is the sum of 3 squares.
29 is a term since phi(29) = 28 is not the sum of 3 squares.
MATHEMATICA
Select[Range[500], SquaresR[3, EulerPhi[#]] == 0 &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Apr 09 2020
STATUS
approved