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Odd-indexed primes: a(n) = prime(2n-1).
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%I #51 Sep 08 2022 08:44:50

%S 2,5,11,17,23,31,41,47,59,67,73,83,97,103,109,127,137,149,157,167,179,

%T 191,197,211,227,233,241,257,269,277,283,307,313,331,347,353,367,379,

%U 389,401,419,431,439,449,461,467,487,499,509,523,547,563

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

%C Appeared as a puzzle in "Stickelers", a nationally distributed feature, by Terry Stickels, Sep 28 2006. - _Franklin T. Adams-Watters_, Sep 28 2006

%C Also every second prime starting with 2. - _Cino Hilliard_, Dec 02 2007

%C Central terms of the triangle in A005145. - _Reinhard Zumkeller_, Aug 05 2009

%H Reinhard Zumkeller, <a href="/A031368/b031368.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A219603(n) / A000040(n). - _Reinhard Zumkeller_, Nov 25 2012

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

%t Table[ Prime[ 2n -1], {n, 52}] (* _Robert G. Wilson v_, Dec 01 2013 *)

%o (Magma) [ NthPrime(2*n-1): n in [1..1000] ]; // _Vincenzo Librandi_, Apr 11 2011

%o (Haskell)

%o a031368 = a000040 . ((subtract 1) . (* 2))

%o a031368_list = map a000040 [1, 3 ..] -- _Reinhard Zumkeller_, Nov 25 2012

%o (PARI) a(n) = prime(2*n-1) \\ _Jianing Song_, Jun 03 2021

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

%Y First differences are A155067.

%K nonn,easy

%O 1,1

%A _Jeff Burch_