It is. http://projecteuler.net/problem=14 http://projecteuler.net/problem=14 Also: "A Modified Collatz sequence": http://projecteuler.net/problem=277 http://p

It is. http://projecteuler.net/problem=14 http://projecteuler.net/problem=14 Also: "A Modified Collatz sequence": http://projecteuler.net/problem=277 http://projecteuler.net/problem=277 There may be others.