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 A171619 #24 Feb 16 2025 08:33:11 %S A171619 5,7,29,67,83,109,173,239,241,251,293,313,337,367,571,613,769,821,877, %T A171619 941,947,1031,1069,1103,1511,1693,1759,1901,2011 %N A171619 Primes in A171490. %C A171619 Terms of sequence are primes in growing order where smallest number of steps m to reach 1 in "3x+1" (or Collatz) problem is a prime too. %D A171619 R. K. Guy, "Collatz's Sequence" in Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, pp. 215-218, 1994. %D A171619 Clifford A. Pickover, Wonders of Numbers, Oxford University Press, pp. 116-118, 2001. %D A171619 Guenther J. Wirsching, The Dynamical System Generated by the 3n+1 Function, Springer-Verlag, Berlin, 1998. %H A171619 Eric Roosendaal, <a href="http://www.ericr.nl/wondrous/classrec.html">3x+1 Class Records</a> %H A171619 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CollatzProblem.html">Collatz Problem</a> %e A171619 (1) 1st Collatz sequence with 5=prime(3) steps starts with 5=prime(3): 5-16-8-4-2-1, gives a(1)=5. %e A171619 (2) 1st Collatz sequence with 7=prime(4) steps starts with 3=prime(2): 3-10-5-16-8-4-2-1, gives a(2)=7. %e A171619 (3) 1st Collatz sequence with 29=prime(10) steps starts with 43=prime(14): 43-130-65-196-98-49-148-74-37-112-56-28-14-7-22-11-34-17-52-26-13-40-20-10-5-16-8-4-2-1, gives a(3)=29. %e A171619 (4) List of prime steps m for above a(n): 5, 3, 43, 167, 233, 41, 937, 14831, 9887, 7963, 73063, 45127, 78791, 225023, 6956969, 10998599, 126357223, 859130059, 2845683047, 322623647, 95592191, 8363817307, 28677246203, 38590505339, 35521451596571, 478672174364191, 1168778549494463, 6376392739978081, 103147916159472367. %Y A171619 Cf. A070905, A033491, A088975, A126727, A060565, A171490. %K A171619 nonn,hard,more %O A171619 1,1 %A A171619 Ulrich Krug (leuchtfeuer37(AT)gmx.de), Dec 13 2009 %E A171619 Missing term a(7)=173 inserted by _Georg Fischer_, Oct 26 2022 %E A171619 a(23)-a(29) (using Eric Roosendaal's data) by _Tyler Busby_, Feb 11 2023