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 A225403 Smallest prime q such that 2*prime(n)*q^prime(n)+1 is also prime. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified February 24 16:16 EST 2024. Contains 370307 sequences. (Running on oeis4.)