OFFSET
1,1
LINKS
L. Mirsky, Summation formula involving arithmetic functions, Duke Mathematical Journal, Vol. 16, No. 2 (1949), pp. 261-272.
FORMULA
a(n) ~ 3*c*n^4 / 8, where c = A206256 = Product_{p prime} (1 - 3/p^2) [Mirsky, 1949, p. 270, formula 30].
MATHEMATICA
Accumulate[Table[EulerPhi[k]*EulerPhi[k+1]*EulerPhi[k+2], {k, 1, 50}]]
PROG
(PARI) a(n) = sum(k=1, n, eulerphi(k)*eulerphi(k+1)*eulerphi(k+2)); \\ Michel Marcus, May 24 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, May 24 2020
STATUS
approved