Salediablo3 2013/11/22 update
Total Paragon Experience less than 7,848 million (Paragon Level less than 100) can check the sheet.
N level (n>=100) need experience (unit is million) is
p(n) = 149.76+1.44(n-100) (n>99)
Reaper of Souls new paragon 100 experience is 7848 million, current is 10454.4 million
When you reach N level (N>=100) Paragon Experience P (million) is
P(n) = 7848+p(101)+p(102)+…+p(n)
= 7848 + 149.76(n-100)+ 1.44(n-100)(n-99)/2
= 7848 + 149.76N + 0.72N(N+1)
In this equal, N=n-100
So N= {-150.48 + SQRT[150.48^2-2.88(7848-P)]}/1.44 = SQRT(42+2.88P)/0.72-104.5
n = SQRT(42+2.88P)/0.72-4.5
Here, P is your Paragon Experience (unit million), n is the total shared Paragon level
For those who only want the results
100*1 = 116 lvl
100*2 = 166 lvl
100*3 = 204 lvl
100*4 = 237 lvl
100*5 = 265 lvl
100*6 = 291 lvl
100*7 = 314 lvl
100*8 = 336 lvl
100*9 = 357 lvl
100*10 = 377 lvl
Someone from Diablofans community has made a sheet about the experience needed for 1-2,000. For your information, there is no cap for Paragon in the new system. There is a huge experience change in the previous 100 level. For the sheet we can see that, every level need 2,147,483,647 experience since 1500 level. If you want to hit 1,000 level, you need 726,480,000,000 XP in total. Click Reaper of Souls Experience Sheet for original Google File.
In the future, you can pass your account to your son and tell him this cause has not been finished. He should continue to strive for. Then there would be news about who is the owner of highest Diablo Paragon Level. If the game is interesting enough, you would stick to it like WOW and play for up to 5 years, you would hit Level 1000 sooner or later. Do not be scared by these figures. We used to think that Paragon level 100 is a dream. But see what happens now. Some players have up to five heroes all up to level 100. Imagine how much time they have spent on this game.
Written by Phebe sal Game Reviewer