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 A127930 #13 Jan 05 2025 19:51:38
%S A127930 3,43,109,163,307,439,541,619,937,1069,1087,1297,1303,1321,1609,1621,
%T A127930 1627,1657,1783,1861,2053,2251,2293,2311,2347,2647,2689,3067,3121,
%U A127930 3319,3373,3457,3499,3511,3517,3607,3637,3769,4051,4057,4219,4363,4561,4723,4813,4903
%N A127930 Terms of A127928 that are prime in A006577.
%C A127930 Through a(9) the terms have the following number of 3x+1 problem steps: 7, 29, 113, 23, 37, 53, 43, 131, 173.
%H A127930 Amiram Eldar, <a href="/A127930/b127930.txt">Table of n, a(n) for n = 1..2000</a>
%H A127930 Douglas J. Shaw, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Papers1/44-3/quartshaw03_2006.pdf">The Pure Numbers Generated by the Collatz Sequence</a>, The Fibonacci Quarterly, Vol. 44, Number 3, August 2006, pp. 194-201.
%F A127930 A127928 = numbers that are both pure hailstone (Collatz) and prime. A127930 = the subset having prime steps to reach 1; given the Collatz rule C(n) = {3n+1, n odd; n/2 if n is even}.
%e A127930 3 is in the set A127930 since the iterative trajectory of 3 has 7 steps: (10, 5, 16, 8, 4, 2, 1) and 7 is prime.
%Y A127930 Cf. A006577, A066903, A127928, A127928, A061641, A127633.
%K A127930 nonn
%O A127930 1,1
%A A127930 _Gary W. Adamson_, Feb 07 2007
%E A127930 More terms from _Amiram Eldar_, Feb 28 2020