OFFSET
0,2
COMMENTS
By definition, all terms are squarefree (A005117).
EXAMPLE
For n=4, we have binomials: 1,4,6,4,1.
To obtain a(4), we form the sums 1[+]4 = 1[+]1 = 2; 2[+]6 = 2; 2[+]4 = 2[+]1 = 3; 3[+]1=1. So a(4)=1.
MATHEMATICA
a7913[n_]:=a7913[n]=Times@@(#[[1]]^Mod[#[[2]], 2])&[Transpose[FactorInteger[n]]];
ab[x_, y_]:=ab[x, y]=a7913[a7913[x]+a7913[y]];
Table[Fold[ab, First[#], Rest[#]]&[Binomial[n, #]&[Range[0, n]]], {n, 0, 50}] (* Peter J. C. Moses, Oct 27 2014 *)
PROG
(PARI) a(n) = {s = 0; for (i=0, n, s = core(core(binomial(n, i)) + core(s))); s; } \\ Michel Marcus, Nov 14 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Oct 27 2014
EXTENSIONS
More terms from Peter J. C. Moses, Oct 27 2014
STATUS
approved