solution for https://fivethirtyeight.com/features/can-you-make-it-to-2023/

trib_contains.py

class TribSequence():
	def __init__(self, a, b, c):
		self.seq = [a, b, c]

	def next_term(self):
		self.seq += [self.seq[-1] + self.seq[-2] + self.seq[-3]]

	def contains(self, num):
		if num in self.seq:
			return True
		if self.seq[-1] > num:
			return False
		self.next_term()
		return self.contains(num)


def smallest_seq_containing(num):
	a,b,c = 0,0,0
	for i in range(1,int(num/2)):
		for j in range(1,i):
			for k in range(1,j):
				t = TribSequence(a+k, b+j, c+i)
				if t.contains(num):
					return (a+k, b+j, c+i)

print(smallest_seq_containing(2023))