OFFSET
1,2
COMMENTS
Dirichlet convolution of [1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,4,0,0,...] with A007425.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
J. S. Rutherford, The enumeration and symmetry-significant properties of derivative lattices, Acta Cryst. A48 (1992), 500-508. See Table 1, Bravais lattice / symmetry Immm.
FORMULA
From Amiram Eldar, Oct 25 2022: (Start):
Multiplicative with a(2) = 3, a(2^e) = 3*(e-2)*(e-1)+7 for e > 1, and a(p^e) = (e+1)*(e+2)/2 if p > 2.
Sum_{k=1..n} a(k) ~ (3/4)*n*log(n)^2 + c_1*n*log(n) + c_2*n, where c_1 = 9*gamma/2 - 3*log(2)/2 - 3/2 and c_2 = 3/2 + 9*gamma*(gamma-1)/2 - 9*gamma*log(2)/2 - 9*gamma_1/2 + 3*log(2)/2 + 5*log(2)^2/2, where gamma is Euler's constant (A001620) and gamma_1 is the 1st Stieltjes constant (A082633). (End)
MAPLE
nmax := 100 :
L := [1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, seq(0, i=1..nmax)] :
MOBIUSi(%) :
MOBIUSi(%) :
MOBIUSi(%) ; # R. J. Mathar, Sep 25 2017
MATHEMATICA
f[p_, e_] := (e + 1)*(e + 2)/2; f[2, 1] = 3; f[2, e_] := 3*(e - 2)*(e - 1) + 7; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Oct 25 2022 *)
PROG
(PARI)
up_to = 10000
t1=direuler(p=2, up_to, 1/(1-X)^3);
t2=direuler(p=2, 2, 1+1*X^2+4*X^4, up_to);
t3=dirmul(t1, t2);
\\ Antti Karttunen, Sep 24 2017, after PARI-code in A145444.
(PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i, 1] == 2, if(f[i, 2] == 1, 3, 3*(f[i, 2]-2)*(f[i, 2]-1)+7), (f[i, 2]+1)*(f[i, 2]+2)/2)); } \\ Amiram Eldar, Oct 25 2022
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
N. J. A. Sloane, Mar 14 2009
STATUS
approved