OFFSET
1,4
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
FORMULA
a(n+2) = Sum a(k), k|n. Shifts left two places under inverse Moebius transformation.
G.f. A(x) satisfies: A(x) = x + x^2 * (1 + A(x) + A(x^2) + A(x^3) + ...). - Ilya Gutkovskiy, May 09 2019
MATHEMATICA
a[n_] := a[n] = Sum[a[k], {k, Divisors[n-2]}]; a[1] = a[2] = 1; Table[a[n], {n, 1, 60}] (* Jean-François Alcover, May 15 2013 *)
PROG
(Haskell)
a007439 n = a007439_list !! (n-1)
a007439_list = 1 : 1 : f 2 where
f x = (sum $ map a007439 $ a027750_row (x - 1)) : f (x + 1)
-- Reinhard Zumkeller, Dec 20 2014
CROSSREFS
KEYWORD
AUTHOR
EXTENSIONS
New description from Christian G. Bower, Oct 15 1998
STATUS
approved