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 A031441 #15 Jul 02 2025 16:01:56
%S A031441 3,5,7,17,11,19,23,109,17,11,19,23,109,17,11,19,23,109,17,11,19,23,
%T A031441 109,17,11,19,23,109,17,11,19,23,109,17,11,19,23,109,17,11,19,23,109,
%U A031441 17,11,19,23,109,17,11,19,23,109,17,11,19,23,109,17,11,19,23,109,17,11,19,23
%N A031441 a(0) = 3; 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 A031441 Harvey P. Dale, <a href="/A031441/b031441.txt">Table of n, a(n) for n = 0..1000</a>
%e A031441 To get a(3) we compute PreviousPrime(7)=5, 5*7-1=34, greatest prime factor of 34 is 17, so a(3)=17.
%t A031441 a[0] = 3; a[n_] := a[n] = FactorInteger[ NextPrime[ a[n-1], -1]*a[n-1] - 1][[-1, 1]]; Table[a[n], {n, 0, 66}] (* _Jean-François Alcover_, Mar 09 2012 *)
%t A031441 NestList[FactorInteger[NextPrime[#,-1]*#-1][[-1,1]]&,3,70] (* _Harvey P. Dale_, Dec 13 2012 *)
%Y A031441 Cf. A034970, A031442.
%K A031441 nonn,easy,nice
%O A031441 0,1
%A A031441 _Yasutoshi Kohmoto_
%E A031441 More terms from _James Sellers_