Answer will be 1431.

Total blocks = 10000

Order of leaf node =

p(12+20) + 12 <= 512, hence p = 15

Order of non leaf =

p'(12) + (p'-1)20 <= 512, hence p' = 16

Now to maximize the nodes we would take min elements in each node

i.e leaf node will get ceil(15/2) = 8 and non leaf will get ceil(16/2) = 8

Hence total nodes at bottom level = 10000/8 = 1250

at one level above 1250/8 = 157

then 157/8 = 20

then 20/8 = 3

then 1 node

Hence total nodes required = 1250 + 157 + 20 + 3 + 1 = **1431**