a element b\c it has no other elements in the equation
The corresponding element is phosphorus.
It is NOT an element, but the Nitride anion. (N^3-).
Radium
Ca
Xe
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Not sure about "completes" because the sequence continues. The next number is 20 and you can verify that by fitting the following cubic equation: u(n) = 5*(-n3 + 36n2 - 257n + 558)/12 for n = 1, 2, 3, 4, ...
zone of differenation
The chemical formula for a nitride ion is N-3.
The last element for which there are claims of discovery is Uus, element 117. That completes the 118 elements on the periodic table.
Let any number be n:- n3/n3 = n*n*n/n*n*n = 1 And in index form: n3/n3 = n3-3 = n0 = 1