This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A359803 #94 Jun 02 2025 15:26:34 %S A359803 1,1,2,1,4,2,1,7,22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1,24,12,6,3, %T A359803 10,5,16,8,4,2,1,35,106,53,160,80,40,20,10,5,16,8,4,2,1,49,148,74,37, %U A359803 112,56,28,14,7,22,11,34,17,52,26,13,40,20,10,5,16,8 %N A359803 a(1) = 1; for n > 1, a(n) = n-1 if a(n-1) = 1, otherwise, apply the '3x+1' function to a(n-1). %e A359803 For n = 5, the sequence so far is (1, 1, 2, 1) a(4) = 1, therefore a(5) = 5-1 = 4. %e A359803 For n = 6, the sequence so far is (1, 1, 2, 1, 4), 4 is not 1, so we apply the '3x+1' function, 4 is even, so we divide it by 2, therefore a(6) = 4/2 = 2. %e A359803 For n = 9, the sequence so far is (1, 1, 2, 1, 4, 2, 1, 7), 7 is not 1, so we apply the '3x+1' function, 7 is odd, so we multiply it by 3 and add 1, therefore a(9) = 3*(7)+1 = 22. %o A359803 (Python) %o A359803 def a(length): %o A359803 sequence = [1] %o A359803 while len(sequence) < length: %o A359803 last_term = sequence[-1] %o A359803 if last_term == 1: %o A359803 next_term = len(sequence) %o A359803 elif last_term % 2 == 0: %o A359803 next_term = last_term // 2 %o A359803 else: %o A359803 next_term = 3 * last_term + 1 %o A359803 sequence.append(next_term) %o A359803 return sequence %Y A359803 Selected rows from A070165. %Y A359803 Cf. A014682. %K A359803 nonn,look,easy %O A359803 1,3 %A A359803 _Wagner Martins_, Jul 17 2023