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PROJECT EULER · #0175

Fractions and Sum of Powers of Two

Statement only · SolvedOriginal problem ↗

Define f(0)=1 and f(n) to be the number of ways to write n as a sum of powers of 2 where no power occurs more than twice.

For example, f(10)=5 since there are five different ways to express 10:
10=8+2=8+1+1=4+4+2=4+2+2+1+1=4+4+1+1.

It can be shown that for every fraction p/q (p>0, q>0) there exists at least one integer n such that f(n)/f(n1)=p/q.

For instance, the smallest n for which f(n)/f(n1)=13/17 is 241.
The binary expansion of 241 is 11110001.
Reading this binary number from the most significant bit to the least significant bit there are 4 one's, 3 zeroes and 1 one. We shall call the string 4,3,1 the Shortened Binary Expansion of 241.

Find the Shortened Binary Expansion of the smallest n for which f(n)/f(n1)=123456789/987654321.

Give your answer as comma separated integers, without any whitespaces.

Write-up coming later

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