Coulomb Operator

Dear all, when I define Coulombs operators for a d shell

OppF0 = NewOperator("U", NF, IndexUp, IndexDn, {1,0,0})
OppF2 = NewOperator("U", NF, IndexUp, IndexDn, {0,1,0})
OppF4 = NewOperator("U", NF, IndexUp, IndexDn, {0,0,1})

what does the last list (for example {1,0,0}) mean?

and why into the program which computes the eigenstates of the coulomb operator at some point I find it written

– Number of allowed Slater integrals is L + 1

SlaterInts [1] = 20

for i = 2, Nk do

  SlaterInts [i] = SlaterInts [i-1] / 2

end

where does that “20” come from?

Thanks in advance

Riccardo