Former McDonald's Worker Does a Number Theory Proof

Number theory classic problem with Sophie Germain's identity. A few days ago I was in my storage room and found my good old McDonald's uniform with the name tag. So many memories rushed back to me after I put it on again after 10+ years. Of course, I will never forget about the teacher who once helped a hopeless kid to get his first job.

Thank you, Mr. Sergio Salas.

10% off with the code "TEESPRINGWELCOME10"

Equipment:
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bprp

[shreyassinha]

Man, your respect in my eyes got doubled, don't know your struggle story, but great efforsta nad hardwork in getting up till here

Best of Luck for future

[aurithrabarua]

Absolutely inspiring
Respect for you 👏👏👏

[grantswallow]

I figured this out without factoring like that. I used 9^4 ends in a 1, and 4^2019 ends in a 4, and 4+1 is 5. Therefore, it is divisible by 5

[SlipperyTeeth]

3:18 I mean, this is just obviously wrong with Pythagorean triples. We're talking about different types of factoring when we bring up prime/composite numbers.

[hmqd]

easier way: 2019^4=1 mod 5 from fermats little theorem, and 4^2019=-1^2019=-1 mod 5 so its divisible by 5

[emanuellandeholm]

n has to be odd or the sum is divisible by two
n has to be a multiple of five or the sum is divisible by five (if it's already odd)
so n = 10k + 5 (5, 15, 25, ...)

I've checked n = 5, 15, ... 105 and no primes so far...

[kaushikmahanta]

Sir we can not the unit digit of 2019^4 is 1 and 4^odd power(here it's 2019) always ends with 4 so the result will definitely be a no which has 5 at its unit place and definitely it's not 5 which is a prime no ;it will be a no divisible by 5 hence not prime

[eshumanohare]

this background music of doraemon is really annoying.