Fibonacci ?? Nope!!

Level 2

What is the 15th term in this sequence?


The answer is 2209.

Niaz Bin Siraj by Niaz Bin Siraj , 24, Bangladesh

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2 solutions

Vineet Golcha
May 21, 2015

this is a triboncci sequence ,i.e.,every term starting from fouth is the sum of the preceding three terms. 1,1,1,3,5,9,17,31,57,105,193,355,653,1201,2209

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You missed 14th term in this sequence. 653+355+193=1201 ... then, 1201+653+355=2209 ........ the 14th term is 1201 but you wrote 1209 and the 15th term is 2209 but you wrote 2214. :)

Niaz Bin Siraj - 6 years ago
Andrew Carratu
Aug 24, 2020

The sequence is basically in the form a n + a n + 1 + a n + 2 = a n + 3 a_n+a_{n+1}+a_{n+2}=a_{n+3}

You just repeatedly add the last 3 numbers in the sequence to get the next number in order to get that the answer is 2209 \fbox{2209}

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