# What's my telephone number?

## Python, 33 bytes

```
f=lambda n:n<2or~-n*f(n-2)+f(n-1)
```

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Uses the recursive formula.

## Oasis, ~~7~~ ~~6~~ 5 bytes

```
àn*+1
```

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```
# to compute the nth telephone number f(n):
à # push the telephone numbers f(n-1) and f(n-2)
n # push n
* # multiply: n * f(n-2)
+ # add: n * f(n-2) + f(n-1)
1 # base case: f(0) = 1
```

## cQuents, 10 bytes

```
=1:Z+Y($-2
```

1-indexed.

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### Explanation

```
=1 first term in sequence is 1
: given n, output nth term in sequence (1-indexed)
each term is
Z+ (n-1) term +
Y (n-2) term *
($-2 (index - 2)
```