A number theory problem by Ραμών Αδάλια

Number Theory Level pending

Determine the next term of the sequence:

2 4 8 16 ? 2\quad 4\quad 8\quad 16\quad ?

32 1 Impossible to tell 8 4 2 0 16

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1 solution

There's infinitely many sequences which begin 2, 4, 8, 16. The fact that the pattern seems to be that a n = 2 n { a }_{ n }={ 2 }^{ n } does not mean it actually is. Let me give a simple counter example:

a n = 1 24 [ ( π 30 ) n 4 + ( 308 10 π ) n 3 + ( 35 π 1074 ) n 2 + ( 1564 50 π ) n + 24 ( π 30 ) ] { a }_{ n }=\frac { 1 }{ 24 } \left[ (\pi -30){ n }^{ 4 }+(308-10\pi ){ n }^{ 3 }+(35\pi -1074){ n }^{ 2 }+(1564-50\pi )n+24(\pi -30) \right]

In this sequence, the first 4 terms are 2, 4, 8, and 16, but the next one is π \pi . Do not trust patterns unless you are able to prove them

Too much effort on that solution mate, it's clearly trivial

Sergi Mlg Sabat - 4 years, 11 months ago

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Nice approach!

Ραμών Αδάλια - 4 years, 11 months ago

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