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Well i noticed a pattern in the function.

f(10000000) = 94688
f(2000000) = 94688
f(400000) = 94688
f(80000) = 94688
f(16000) = 74688

you see that the inputs has the same answers. We can basicly skip a lot of values. At 16000 he begin to lose detail because it becomes smaller then the filter(10^5).

I made a table as following:

1000000000000
 200000000000
  40000000000
   8000000000
   1600000000
    320000000
     64000000
     12800000
      2560000

basicly f(1000000000000) is same as f(2560000)
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from https://projecteuler.net/thread=160;page=7