A117997 Sum_{d|n} a(d) = n for n = 3^m (m >= 0) and for other n the sum is zero; i.e., the Möbius transform of [1, 0, 3, 0, 0, 0, 0, 0, 9, 0,...].

1, -1, 2, 0, -1, -2, -1, 0, 6, 1, -1, 0, -1, 1, -2, 0, -1, -6, -1, 0, -2, 1, -1, 0, 0, 1, 18, 0, -1, 2, -1, 0, -2, 1, 1, 0, -1, 1, -2, 0, -1, 2, -1, 0, -6, 1, -1, 0, 0, 0, -2, 0, -1, -18, 1, 0, -2, 1, -1, 0, -1, 1, -6, 0, 1, 2, -1, 0, -2, -1, -1, 0, -1, 1, 0, 0, 1, 2, -1, 0, 54, 1, -1, 0, 1, 1, -2, 0, -1, 6, 1, 0, -2, 1, 1, 0, -1, 0, -6, 0, -1, 2, -1, 0, 2

Offset: 1

Author

Paul D. Hanna, Apr 08 2006

Keywords

• sign

Comments

From Petros Hadjicostas, Jul 26 2020: (Start)

For p prime >= 2, Petrogradsky (2003) defined the multiplicative functions 1_p and mu_p in the following way:

1_p(n) = 1 when gcd(n,p) = 1 and 1_p(n) = 1 - p when gcd(n,p) = p;

mu_p(n) = mu(n) when gcd(n,p) = 1 and mu_p(n) = mu(m)*(p^s - p^(s-1)) when n = m*p^s with gcd(m,p) = 1 and s >= 1.

We have 1_2(n) = A062157(n), 1_3(n) = A061347(n), A067856(n) = mu_2(n), and a(n) = mu_3(n) for n >= 1.

Some of the results by other contributors here and in A067856 can be generalized:

(i) Rogel's (1897) formula for A067856 becomes Sum_{d | n} 1_p(d) * mu_p(n/d) = 0 for n > 1. Thus, 1_p is the Dirichlet inverse of mu_p.

(ii) R. J. Mathar's Dirichlet g.f. for mu_p becomes 1/(zeta(s) * (1 - p^(1-s))). The Dirichlet g.f. for 1_p is zeta(s) * (1 - p^(1-s)).

(iii) Benoit Cloitre's formula becomes 1 = Sum_{k=1..n} mu_p(k)*g_p(n/k), where g_p(x) = floor(x) - p*floor(x/p) = floor(x) mod p.

(iv) Paul D. Hanna's formula becomes Sum_{n >= 1} (mu_p(n)/n)*log((1 - x^(n*p))/(1 - x^n)) = x.

(v) The definition in the name of the sequence a(n) generalizes to Sum_{d | n} mu_p(d) = n, if n = p^s for s >= 0, and = 0, otherwise. Thus, mu_p(n) = Sum_{p^k | n, k >= 0} mu(n/p^k)*p^k. That is, (mu_p(n): n >= 1) is the Möbius transform of the sequence (b_p(n): n >= 1), where b_p(n) = p^k, if n = p^k for k >= 0, and b_p(n) = 0, otherwise.

(vi) We have the Lambert series Sum_{n >= 1} mu_p(n)*x^n/(1 - x^n) = Sum_{k >= 0} p^k*x^(p^k) = x + p*x^p + p^2*x^(p^2) + ..., which generalizes one of the formulas by Peter Bala in A067856.

(vii) By differentiating both sides of (iv) w.r.t. x and multiplying both sides by x, we get Sum_{n >= 1} mu_p(n)*(x^n + 2*x^(2*n) + ... + (p-1)*x^(n*(p-1)))/(1 + x^n + x^(2*n) + ... + x^(n*(p-1))) = x, which generalizes another one of Peter Bala's formulas in A067856. It can be thought as a "generalized Lambert series".

(viii) Dividing both sides of (vi) by x and integrating w.r.t. x from 0 to y, we get -Sum_{n >= 1} (mu_p(n)/n)*log(1 - y^n) = Sum_{k >= 0} y^(p^k) = y + y^p + y^(p^2) + y^(p^3) + ...

(ix) Obviously, f(n) = Sum_{d | n} 1_p(n/d)*g(d) if and only if g(n) = Sum_{d | n} mu_p(n/d)*f(d). (End)

Links

• Antti Karttunen, Table of n, a(n) for n = 1..59049
• Peter Bala, A signed Dirichlet product of arithmetical functions.
• V. M. Petrogradsky, Witt's formula for restricted Lie algebras, Advances in Applied Mathematics, 30 (2003), 219-227.
• Eric Weisstein's World of Mathematics, Möbius Transform.

Crossrefs

Cf. A061347, A062157, A067856.

Programs

PARI

{a(n)=if(n==1,1,-n*polcoeff(x+sum(k=1,n-1,a(k)/k*subst(log(1+x+x^2+x*O(x^n)),x,x^k+x*O(x^n))),n))}

PARI

A117997(n) = sumdiv(n,d,moebius(n/d)*if((3^valuation(d,3))==d,d,0)); \\ Antti Karttunen, Jan 15 2025

Formula

G.f.: x = Sum_{n >= 1} (a(n)/n)*log(1 + x^n + x^(2*n)).

1 = Sum_{k=1..n} a(k)*g(n/k), where g(x) = floor(x) - 3*floor(x/3). [Benoit Cloitre, Nov 11 2010]

From Petros Hadjicostas, Jul 26 2020: (Start)

a(n) = Sum_{3^k | n, k >= 0} mu(n/3^k)*3^k.

Dirichlet g.f.: 1/(zeta(s)*(1 - 3^(1-s))).

The sequence is the Dirichlet inverse of A061347.

Sum_{n >= 1} a(n)*x^n/(1 - x^n) = x + 3*x^3 + 9*x^9 + 27*x^27 + 81*x^81 + ...

Sum_{n >= 1} a(n)*(x^n + 2*x^(2*n))/(1 + x^n + x^(2*n)) = x.

-Sum_{n >= 1} (a(n)/n)*log(1 - x^n) = x + x^3 + x^9 + x^27 + x^81 + ... (End)

Extensions

Offset changed to 1 by Petros Hadjicostas, Jul 26 2020