Just Like Fibonacci

Number Theory Level 4

I have a sequence similar to the Fibonacci Sequence.

1 , 1 , 1 , 3 , 5 , 9 , 17 , 31 , 57 , 105 , 193 , . . . 1,1,1,3,5,9,17,31,57,105,193,...

Each term is the sum of of the previous three terms. How many of the first 2014 2014 numbers have a 9 9 in the units digit?


The answer is 389.

Alex Segesta by Alex Segesta , 20, USA

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1 solution

Anand Raj
Mar 4, 2014

I Found that after 31 terms the unit digit repeated........In 31 terms were 6 times.......

in 31x64 = 1984 terms ===== 6x64 = 384 9s

In remaining 30 terms 5 9s........

So total 389 times 9

8 Helpful 0 Interesting 0 Brilliant 0 Confused

Correct answer is 380and not 389

sangeet aggarwal - 7 years, 1 month ago

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