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Fibonacci numbers: Difference between revisions
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==Mathematics== | ==Mathematics== | ||
The ratio <math> \frac {F_n}{F_{n+1}} \ </math> approaches the | The ratio <math> \frac {F_n}{F_{n+1}} \ </math> approaches the golden ratio as <math>n</math> approaches infinity. | ||
[[File:PascalTriangleFibanacci.png|thumb|right|360px|The Fibonacci numbers are the sums of the "shallow" diagonals (shown in red) of | [[File:PascalTriangleFibanacci.png|thumb|right|360px|The Fibonacci numbers are the sums of the "shallow" diagonals (shown in red) of Pascal's triangle.]] | ||
The Fibonacci numbers occur in the sums of "shallow" diagonals in | The Fibonacci numbers occur in the sums of "shallow" diagonals in Pascal's triangle. | ||
:<math>F_n = \sum_{k=0}^{\left\lfloor\frac{n-1}{2}\right\rfloor} \binom{n-k-1}{k}</math> | :<math>F_n = \sum_{k=0}^{\left\lfloor\frac{n-1}{2}\right\rfloor} \binom{n-k-1}{k}</math> | ||
Counting the number of ways of writing a given number <math>n</math> as an ordered sum of 1s and 2s (called | Counting the number of ways of writing a given number <math>n</math> as an ordered sum of 1s and 2s (called compositions); there are <math>F_{n+1}</math> ways to do this. For example, if <math>n = 5</math>, then <math>F_{n+1} = F_{6} = 8</math> counts the eight compositions summing to 5: | ||
<math>1+1+1+1+1 = 1+1+1+2 = 1+1+2+1 = 1+2+1+1 = 2+1+1+1 = 2+2+1 = 2+1+2 = 1+2+2</math> | <math>1+1+1+1+1 = 1+1+1+2 = 1+1+2+1 = 1+2+1+1 = 2+1+1+1 = 2+2+1 = 2+1+2 = 1+2+2</math> | ||