A031368 Odd-indexed primes: a(n) = prime(2n-1).

2, 5, 11, 17, 23, 31, 41, 47, 59, 67, 73, 83, 97, 103, 109, 127, 137, 149, 157, 167, 179, 191, 197, 211, 227, 233, 241, 257, 269, 277, 283, 307, 313, 331, 347, 353, 367, 379, 389, 401, 419, 431, 439, 449, 461, 467, 487, 499, 509, 523, 547, 563

Offset: 1

Author

Jeff Burch

Keywords

• nonn
• easy

Comments

Appeared as a puzzle in "Stickelers", a nationally distributed feature, by Terry Stickels, Sep 28 2006. - Franklin T. Adams-Watters, Sep 28 2006

Also every second prime starting with 2. - Cino Hilliard, Dec 02 2007

Central terms of the triangle in A005145. - Reinhard Zumkeller, Aug 05 2009

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A031215 (even-indexed primes), A005408.

First differences are A155067.

Programs

Haskell

a031368 = a000040 . ((subtract 1) . (* 2))
a031368_list = map a000040 [1, 3 ..]  -- Reinhard Zumkeller, Nov 25 2012

Magma

[ NthPrime(2*n-1): n in [1..1000] ]; // Vincenzo Librandi, Apr 11 2011

Maple

A031368 := n->ithprime(2*n-1): seq(A031368(n), n=1..100);

Mathematica

Table[ Prime[ 2n -1], {n, 52}] (* Robert G. Wilson v, Dec 01 2013 *)

PARI

a(n) = prime(2*n-1) \\ Jianing Song, Jun 03 2021

Formula

a(n) = A219603(n) / A000040(n). - Reinhard Zumkeller, Nov 25 2012