A031215 - OEIS

A031215

Even-indexed primes: a(n) = prime(2n).

3, 7, 13, 19, 29, 37, 43, 53, 61, 71, 79, 89, 101, 107, 113, 131, 139, 151, 163, 173, 181, 193, 199, 223, 229, 239, 251, 263, 271, 281, 293, 311, 317, 337, 349, 359, 373, 383, 397, 409, 421, 433, 443, 457, 463, 479, 491, 503, 521, 541, 557, 569

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OFFSET

1,1

COMMENTS

Also every second odd prime. - Cino Hilliard, Dec 02 2007

If n > 1, then a(n) is less than, and asymptotic to, the n-th Ramanujan prime R_n = A104272(n). Research questions on the difference R_n - a(n) are at A104272. - Jonathan Sondow, Dec 16 2013

LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A104272(n) - A233739(n). - Jonathan Sondow, Dec 16 2013

a(n) = A105720(n) - A161463(n). - Torlach Rush, May 31 2021

MAPLE

A031215 := n->ithprime(2*n);

MATHEMATICA

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

PROG

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

(PARI) a(n)=prime(2*n) \\ Charles R Greathouse IV, Jul 02 2013