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 A031442 #16 May 26 2025 11:24:12 %S A031442 13,71,41,379,23561,5431,20269,89,1231,44497,329952671,36583,1126159, %T A031442 90209117,14095897,15272393,13887359,256460794943, %U A031442 2740505805180429880723,1591234463080874838018721796071210709 %N A031442 a(0) = 13; for n > 0, a(n) is the greatest prime factor of PreviousPrime(a(n-1))*a(n-1)-1 where PreviousPrime(prime(k))=prime(k-1). %H A031442 Tyler Busby, <a href="/A031442/b031442.txt">Table of n, a(n) for n = 0..21</a> %t A031442 NestList[FactorInteger[#*NextPrime[#,-1]-1][[-1,1]]&,13,20] (* _Harvey P. Dale_, May 26 2025 *) %Y A031442 Cf. A031441. %K A031442 nonn %O A031442 0,1 %A A031442 _Yasutoshi Kohmoto_ %E A031442 More terms from Kok Seng Chua (chuaks(AT)ihpc.nus.edu.sg), May 23 2000. a(19) and a(20) pass the strong pseudoprime test for many bases. %E A031442 Edited by _T. D. Noe_, Oct 30 2008