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a(n) = largest prime <= 2a(n-1), with a(0)=1.
2

%I #17 Sep 29 2019 14:15:38

%S 1,2,3,5,7,13,23,43,83,163,317,631,1259,2503,5003,9973,19937,39869,

%T 79699,159389,318751,637499,1274989,2549951,5099893,10199767,20399531,

%U 40799041,81598067,163196129,326392249,652784471,1305568919,2611137817

%N a(n) = largest prime <= 2a(n-1), with a(0)=1.

%C Equals 1 followed by A006992.

%C This is a complete sequence (cf. A075058).

%H Harvey P. Dale, <a href="/A185231/b185231.txt">Table of n, a(n) for n = 0..1000</a>

%t np[n_]:=Module[{p=NextPrime[2n]},If[p<=2n,p,NextPrime[p,-1]]]; NestList[ np,1,40] (* _Harvey P. Dale_, Sep 29 2019 *)

%o (PARI) lista(nn) = {p = 1; for (n = 1, nn, print1(p, ", "); p = precprime(2*p););} \\ _Michel Marcus_, Aug 26 2013

%Y Cf. A006992, A075058.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Jan 24 2012, following a suggestion from Frank M Jackson.