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PROJECT EULER · #0153

Investigating Gaussian Integers

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As we all know the equation x2=1 has no solutions for real x.
If we however introduce the imaginary number i this equation has two solutions: x=i and x=i.
If we go a step further the equation (x3)2=4 has two complex solutions: x=3+2i and x=32i.
x=3+2i and x=32i are called each others' complex conjugate.
Numbers of the form a+bi are called complex numbers.
In general a+bi and abi are each other's complex conjugate.

A Gaussian Integer is a complex number a+bi such that both a and b are integers.
The regular integers are also Gaussian integers (with b=0).
To distinguish them from Gaussian integers with b0 we call such integers "rational integers."
A Gaussian integer a+bi is called a divisor of a rational integer n if the result na+bi is also a Gaussian integer.
If for example we divide 5 by 1+2i we can simplify 51+2i in the following manner:
Multiply numerator and denominator by the complex conjugate of 1+2i: 12i.
The result is 51+2i=51+2i12i12i=5(12i)1(2i)2=5(12i)1(4)=5(12i)5=12i.
So 1+2i is a divisor of 5.
Note that 1+i is not a divisor of 5 because 51+i=5252i.
Note also that if the Gaussian Integer (a+bi) is a divisor of a rational integer n, then its complex conjugate (abi) is also a divisor of n.

In fact, 5 has six divisors such that the real part is positive: {1,1+2i,12i,2+i,2i,5}.
The following is a table of all of the divisors for the first five positive rational integers:

n Gaussian integer divisors
with positive real part
Sum s(n) of
these divisors
111
21,1+i,1i,25
31,34
41,1+i,1i,2,2+2i,22i,413
51,1+2i,12i,2+i,2i,512

For divisors with positive real parts, then, we have: n=15s(n)=35.

n=1105s(n)=17924657155.

What is n=1108s(n)?

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