What is the next number in this series?

4,12,84,3612....

I never was there, I am always to be.
You have never ever seen me, not ever you will.
Yet I am the confidence of everyone.

Who Am I?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

Can you divide the below-given shape into four equal and identical pieces?

The picture shows the dice results in each couple of throws. If they are actually following a pattern, can you find out the missing one?