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%I #39 Feb 03 2023 20:10:16
%S 3,5,7,1321,11,13,43,17,19,61,23,1321,79,29,31,97,3571,37,571,41,43,
%T 4621,47,337,151,53,271,21217561,59,61,47059,29761,67,1021,71,73,223,
%U 6917,79,241,83,421,6221671,89,631,277,23971,97,1471,101,103,313,107,109,331
%N Start with k=2*n, and until k+1 is prime, apply the map k -> k*(least prime factor of (k+1)); then a(n) = k+1, or 0 if k+1 never reaches a prime.
%C a(126) is unknown; it's known to either be 0 or have more than 152 digits.
%C a(126) has 277 digits. - _J. Lowell_, Jan 01 2023
%C a(161) is unknown; it is either 0 or has more than 333 digits. - _J. Lowell_ and _Sean A. Irvine_, Feb 04 2023
%H Sean A. Irvine, <a href="/A288212/b288212.txt">Table of n, a(n) for n = 1..160</a>
%H Sean A. Irvine <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a288/A288212.java">Java program</a> (github)
%e a(17) = 3571 because:
%e 34 + 1 = 35 is composite with smallest prime factor 5, and 34*5 = 170;
%e 170 + 1 = 171 is composite with smallest prime factor 3, and 170*3 = 510;
%e 510 + 1 = 511 is composite with smallest prime factor 7, and 510*7 = 3570;
%e 3570 + 1 = 3571 is prime.
%e The first term of A152466 that is one less than a prime is A152466(39); a(126) = A152466(39) + 1.
%e If A359444 has a term k that is one less than a prime, then a(161) = k + 1; otherwise, a(161) = 0.
%o (PARI) a(n) = {my(x = 2*n); while (! isprime(x+1), x = x*vecmin(factor(x+1)[,1]);); x+1;} \\ _Michel Marcus_, Jun 07 2017
%Y Cf. A152466, A359444.
%K nonn
%O 1,1
%A _J. Lowell_, Jun 06 2017
%E More terms from _Michel Marcus_, Jun 07 2017
%E Name simplified by _Jon E. Schoenfield_, Jan 01 2023
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