A185231 a(n) = largest prime <= 2a(n-1), with a(0)=1.

1, 2, 3, 5, 7, 13, 23, 43, 83, 163, 317, 631, 1259, 2503, 5003, 9973, 19937, 39869, 79699, 159389, 318751, 637499, 1274989, 2549951, 5099893, 10199767, 20399531, 40799041, 81598067, 163196129, 326392249, 652784471, 1305568919, 2611137817

Offset: 0

Author

N. J. A. Sloane, Jan 24 2012, following a suggestion from Frank M Jackson

Keywords

• nonn

Comments

Equals 1 followed by A006992.

This is a complete sequence (cf. A075058).

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A006992, A075058.

Programs

Mathematica

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

PARI

lista(nn) = {p = 1; for (n = 1, nn, print1(p, ", "); p = precprime(2*p););} \\ Michel Marcus, Aug 26 2013