OFFSET
1,2
COMMENTS
LINKS
Eckford Cohen, Arithmetical functions associated with the unitary divisors of an integer, Mathematische Zeitschrift, Vol. 74, No. 1 (1960), pp. 66-80.
R. Sitaramachandrarao and D. Suryanarayana, On Sum_{n<=x} sigma*(n) and Sum_{n<=x} phi*(n), Proceedings of the American Mathematical Society, Vol. 41, No. 1 (1973), pp. 61-66.
FORMULA
a(n) = Sum_{i=1..n} A047994(i).
a(n) ~ alpha * n^2/2 + O(n*log^2(n)) where alpha = Product_{p prime} (1 - 1/(p*(p+1))) = 0.704442... (A065463). - Amiram Eldar, Dec 18 2018
EXAMPLE
a(7) = 1 + 1 + 2 + 3 + 4 + 2 + 6 = 19.
MATHEMATICA
uphi[1] = 1; uphi[n_] := Times @@ (-1 + Power @@@ FactorInteger[n]); s = 0; Accumulate[Array[uphi, 60]] (* Amiram Eldar, Dec 18 2018*)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, May 12 2010
STATUS
approved