OFFSET
4,2
REFERENCES
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Marius A. Burtea, Table of n, a(n) for n = 4..10000
H. W. Gould, Binomial coefficients, the bracket function and compositions with relatively prime summands, Fib. Quart. 2(4) (1964), 241-260.
N. J. A. Sloane, Transforms
FORMULA
Möbius transform of C(n-1,3).
G.f.: Sum_{k>=1} mu(k) * x^(4*k) / (1 - x^k)^4. - Ilya Gutkovskiy, Feb 05 2020
MAPLE
with(numtheory):
a:= n-> add(mobius(n/d)*binomial(d-1, 3), d=divisors(n)):
seq(a(n), n=4..50); # Alois P. Heinz, Feb 05 2020
MATHEMATICA
a[n_] := Sum[Boole[Divisible[n, k]] MoebiusMu[n/k] Binomial[k - 1, 3], {k, 1, n}]; Table[a[n], {n, 4, 51}] (* Jean-François Alcover, Feb 11 2016 *)
PROG
(Magma) [&+[MoebiusMu(n div d)*Binomial(d-1, 3):d in Divisors(n)]:n in[4..49]]; // Marius A. Burtea, Feb 08 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset changed to 4 by Ilya Gutkovskiy, Feb 05 2020
STATUS
approved