138 Special isosceles triangles.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 22 October 2017
# https://github.com/trizen

# Runtime: 0.126s

# https://projecteuler.net/problem=138

# See also:
#   https://oeis.org/A007805

say sum(1..12, {|n|
    fibonacci(6*n + 3) / 2
})