CMR : nếu $1+2^{n^{n}}+4^{n^{n}}$ là số nguyên tố , n nguyên dương thì $n^{n}=3^{k^{k}}$
CMR : nếu $1+2^{n^{n}}+4^{n^{n}}$ là số nguyên tố , n nguyên dương thì $n^{n}=3^{k^{k}}$
#1
Đã gửi 09-09-2013 - 10:37
- Zaraki, bangbang1412, stronger steps 99 và 1 người khác yêu thích
#2
Đã gửi 09-09-2013 - 11:53
CMR : nếu $1+2^{n^{n}}+4^{n^{n}}$ là số nguyên tố , n nguyên dương thì $n^{n}=3^{k^{k}}$
Lời giải. Đặt $n^n=l$ cho nó đơn giản. Đặt tiếp $l=3^m \cdot o$ với $m,o \in \mathbb{N}, \; o \ge 1, 3 \nmid o$. Khi đó thì $A=1+2^l+4^l=1+(2^{3^m})^o+(2^{3^m})^{2o}$.
Vì $(2^{3^m})^2+2^{3^m}+1| 1+(2^{3^m})^o+(2^{3^m})^{2o}$ nên để $A$ là số nguyên tố thì $(2^{3^m})^2+2^{3^m}+1=1+(2^{3^m})^o+(2^{3^m})^{2o}$ hay $o=1$. Vậy $n^n=3^m$. Vậy $n=3^k$. Ta suy ra $n^n=(3^k)^{3^k}$.
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Discovery is a child’s privilege. I mean the small child, the child who is not afraid to be wrong, to look silly, to not be serious, and to act differently from everyone else. He is also not afraid that the things he is interested in are in bad taste or turn out to be different from his expectations, from what they should be, or rather he is not afraid of what they actually are. He ignores the silent and flawless consensus that is part of the air we breathe – the consensus of all the people who are, or are reputed to be, reasonable.
Grothendieck, Récoltes et Semailles (“Crops and Seeds”).
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