A225403 Smallest prime q such that 2*prime(n)*q^prime(n)+1 is also prime.

2, 3, 7, 5, 7, 41, 283, 3, 127, 11161, 1427, 17, 8011, 821, 607, 2161, 4903, 509, 1607, 127, 11261, 8273, 12037, 58207, 419, 11491, 2153, 1789, 9059, 67843, 29, 5641, 1999, 2459, 1699, 15299, 35747, 2531, 10987, 26497, 36781, 719, 24709, 13721, 29803, 1049

Offset

1,1

Links

Pierre CAMI, Table of n, a(n) for n = 1..250

Example

2*2*2^2+1 = 17 prime so a(1) = 2,
2*3*2^3+1 = 49 composite,
2*3*3^3+1 = 163 prime so a(2) = 3,
2*5*2^5+1 = 321 composite,
2*5*3^5+1 = 2431 composite,
2*5*5^5+1 = 31251 composite,
2*5*7^5+1 = 168071 prime so a(3) = 7.

Prog

(PFGW & SCRIPTIFY)
SCRIPT
DIM n, 0
DIM k
DIM q
DIM pp
DIMS t
OPENFILEOUT myfile, a(n).txt
LABEL a
SET n, n+1
IF n>250 THEN END
SET k, 0
LABEL b
SET k, k+1
SET q, p(k)
SETS t, %d, %d\,; n; q
SET pp, 2*p(n)*q^p(n)+1
PRP pp, t
IF ISPRP THEN GOTO c
GOTO b
LABEL c
WRITE myfile, t
GOTO a
(PARI) a(n) = my(q=2); while(!isprime(2*prime(n)*q^prime(n)+1), q = nextprime(q+1)); q; \\ Michel Marcus, Sep 23 2019

Crossrefs

Sequence in context: A357579 A334126 A341717 * A069786 A128804 A223702

Adjacent sequences: A225400 A225401 A225402 * A225404 A225405 A225406

Keyword

nonn

Author

Pierre CAMI, May 13 2013

Status

approved