What are the 10 most abundant elements in the universe by number of atomic nuclei?
All right, so I took the first list on wikipedia listing the 10 most common elements by mass in parts per million, and did what Rob recommended and here's what I got.

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe

Hydrogen - 739000amu(H)/1amu(H)=739000 H atoms 

Helium - 240000amu(He)/4amu(He)=60000 He atoms

Oxygen - 10400amu(O)/16amu(O)=650 O atoms 

Carbon - 4600amu(C)/12amu(C)=383 C atoms

Neon - 1340amu(Ne)/20.1amu(Ne)=66 Ne atoms 

Iron - 1090amu(Fe)/55.845amu(Fe)=19.5 Fe atoms 

Nitrogen - 960amu(N)/14amu(N)=68.5 N atoms 

Silicon - 650amu(Si)/28.1amu(Si)=23 Si atoms

Magnesium, - 580amu(Mg)/24.3amu(Mg)=24 Mg atoms 

Sulfur - 440amu(S)/32.1amu(S)=13.7 S atoms 

So therefore, the 10 most common elements in the universe by atom, with the relative ratios between them, is;

1.Hydrogen (739000)
2.Helium (60000)
3.Oxygen (650)
4.Carbon (383)
5.Nitrogen (68.5)
6.Neon (66)
7.Magnesium (24)
8.Silicon (23)
9.Iron (19.5)
10.Sulfur (13.7)

If anyone sees a mistake that I made with my reasoning or calculations then please point it out.