$Pattern+Chemistry→Fun$

See that the sequence given in the pic is actually $B,C,F ,H , I$ (Relating them to the atomic number). Thus we see that the sequence is related to " $\color{#D61F06}{\textbf{english alphabets}}$ " more than numbers. In the periodic table, we have the following "English Alphabets" arriving single, they're

$\color{#3D99F6}{\textbf{H,B,C,N,O,F,P,S,K,V,Y,I,W,U}}$ .

(respectively standing for Hydrogen,Boron,Carbon,Nitrogen,Oxygen,Fluorine,Phosphorus,Sulphur, Potassium,Vanadium,Yttrium,Iodine,Tungsten,Uranium) .

---

Out of them, $B,C,F,H,I$ are given in question with their atomic numbers, hence the answer will be product of atomic numbers of them remaining ones ! That will be

$\displaystyle \prod_{i=1}^9 x_i = 7\times 8\times 15\times 16\times 19\times 23\times 39\times 74\times 92$

(I don't know what order you want them to be, but product will be just product, order of the elements won't matter, $\color{#20A900}{right ?}$ ) Just use Wolfram now to multiply the numbers...

Hence the answer is $\Huge{\color{#3D99F6}{\boxed{1559426319360}}}$

Imgur

The series of numbers shown in this puzzle- 5, 6, 9, 1 & 53 - are the atomic numbers of the elements Boron, Carbon, Fluorine, Hydrogen and Iodine respectively. These elements have the chemical symbols B, C, F, H and I. They are thus the elements whose chemical symbol is a single letter, arranged in alphabetical order according to the symbol. The series continues with the elements Potassium, Nitrogen, Oxygen, Phosphorus, Sulfur, Uranium, Vanadium, Tungsten and Yttrium. The question asks for the product of the unknown atomic numbers and the answer is therefore 19 x 7 x 8 x 15 x 16 x 92 x 23 x 74 x 39 which is equal to 1559426319360. This number is too large to be calculated on some pocket calculators, requiring a little ingenuity (for example, subtraction of 1.55 x 1012 reveals the last 10 digits) or the use of a computer program that allows a larger number of digits.