OFFSET
0,2
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
Alois P. Heinz, Table of n, a(n) for n = 0..1000
E. N. Gilbert and J. Riordan, Symmetry types of periodic sequences, Illinois J. Math., 5 (1961), 657-665.
FORMULA
a(n) ~ 4^(n-1) / n. - Cedric Lorand, Apr 18 2022
MAPLE
with(numtheory):
a:= n-> `if`(n=0, 1, add(phi(2*d)*2^(2*n/d), d=divisors(2*n))/(4*n)):
seq(a(n), n=0..20); # Alois P. Heinz, Mar 25 2012
MATHEMATICA
a[n_] := Sum[ EulerPhi[2d]*2^(2n/d), {d, Divisors[2n]}]/(4n); a[0]=1; Table[a[n], {n, 0, 27}] (* Jean-François Alcover, Sep 13 2012, after Alois P. Heinz *)
PROG
(Haskell)
a000116 n = a000116_list !! n
a000116_list = bis a000013_list where bis (x:_:xs) = x : bis xs
-- Reinhard Zumkeller, Jul 08 2013
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
EXTENSIONS
More terms from David W. Wilson, Jan 13 2000
STATUS
approved