# Stern-Brocot sequence

``````# Declare a function to generate the Stern-Brocot sequence
func stern_brocot {
var list = [1, 1]
{
list.append(list+list, list)
list.shift
}
}

# Show the first fifteen members of the sequence.
say 15.of(stern_brocot()).join(' ')

# Show the (1-based) index of where the numbers 1-to-10 first appears
# in the sequence, and where the number 100 first appears in the sequence.
for i (1..10, 100) {
var index = 1
var generator = stern_brocot()
while (generator() != i) {
++index
}
say "First occurrence of #{i} is at index #{index}"
}

# Check that the greatest common divisor of all the two consecutive
# members of the series up to the 1000th member, is always one.
var generator = stern_brocot()
var (a, b) = (generator(), generator())
{
assert_eq(gcd(a, b), 1)
a = b
b = generator()
} * 1000

say "All GCD's are 1"
``````

#### Output:

``````1 1 2 1 3 2 3 1 4 3 5 2 5 3 4
First occurrence of 1 is at index 1
First occurrence of 2 is at index 3
First occurrence of 3 is at index 5
First occurrence of 4 is at index 9
First occurrence of 5 is at index 11
First occurrence of 6 is at index 33
First occurrence of 7 is at index 19
First occurrence of 8 is at index 21
First occurrence of 9 is at index 35
First occurrence of 10 is at index 39
First occurrence of 100 is at index 1179
All GCD's are 1
``````