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September 26th, 2016, 06:06 PM   #1
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Stretched numbers : closed formula

Hi,

Each time I post something controversial or insulting you are in hurry to answer. But when it comes to mathematics you become silent like fishes under the sea.
I have seen very interesting post in french here :
Enigme Nombres serrés @ Prise2Tete

He defines (Nodgim is his nickname) les nombres serres (stretched numbers) as the composite numbers a*b where b<=2a and b>=a
2=1*2, 6=2*3,9=3*3, 20=4*5 etc...are all stretched numbers.

1. Can you find all the stretched numbers less or equal to 10.000?
2. Someone gave on the same thread a formula not correct can you find a closed formula for those numbers?
3. Can you find a formula for counting all the composite numbers but the stretched numbers?
4. If you find a closed formula for both kind of composite numbers you will have the first closed formula counting exactly the prime numbers.
Anyone interested could contribute.

Now I promise that I will never put my feet here because I know that no one here is really interested in mathematics.
You have big big big problem with yourselves.
My advise : do other things than mathematics (art, business, etc...).
FORGET ABOUT MATHS YOU ARE NOT INTERESTED AT ALL BY MATHEMATICS.
GOOD BYE AND GOOD LUCK!
I CUT OFF INTERNET ONCE FOR ALL.
Thanks from Joppy
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