OFFSET
1,12
LINKS
R. Zumkeller, Table of n, a(n) for n = 1..10000
Peter Luschny, Zumkeller Numbers
EXAMPLE
a(100)=#{6,12,20,24,28,30,40,42,48,54,56,60,66,70,78,80,84,88,90,96}=20;
a(1000000)=229026, by T. D. Noe.
MATHEMATICA
ZumkellerQ[n_] := Module[{d = Divisors[n], t, ds, x}, ds = Total[d]; If[Mod[ds, 2] > 0, False, t = CoefficientList[Product[1 + x^i, {i, d}], x]; t[[1 + ds/2]] > 0]];
b[n_] := Boole[ZumkellerQ[n]];
Array[b, 100] // Accumulate (* Jean-François Alcover, Apr 30 2017, after T. D. Noe *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 19 2010
STATUS
approved