OFFSET
1,2
COMMENTS
Compare the g.f. of this sequence to the following identities:
. Sum_{n>=1} -moebius(2*n)*x^n/(1-x^n)^2 = Sum_{n>=1} phi(2*n)*x^n;
. Sum_{n>=1} -moebius(2*n)*x^n/(1-x^n) = Sum_{n>=0} x^(2^n).
LINKS
Paul D. Hanna, Table of n, a(n) for n = 1..8200
FORMULA
a(2^n) = 2^(n-1)*(1 + 2^n) for n>=1.
EXAMPLE
G.f.: A(x) = x + 3*x^2 + 5*x^3 + 10*x^4 + 14*x^5 + 18*x^6 + 27*x^7 +...
where A(x) = x/(1-x^1)^3 + 0*x^2/(1-x^2)^3 - x^3/(1-x^3)^3 + 0*x^4/(1-x^4)^3 - x^5/(1-x^5)^3 + 0*x^6/(1-x^6)^3 - x^7/(1-x^7)^3 + 0*x^8/(1-x^8)^3 + 0*x^9/(1-x^9)^3 + 0*x^10/(1-x^10)^3 - x^11/(1-x^11)^3 +...
PROG
(PARI) {a(n)=polcoeff(sum(m=1, n, -moebius(2*m)*x^m/(1-x^m+x*O(x^n))^3), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 08 2011
STATUS
approved