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A249382 Smallest odd prime Q such that Q*2^prime(n)-1 is also a prime number. 3
3, 3, 7, 3, 3, 31, 7, 61, 13, 7, 43, 31, 19, 3, 31, 307, 733, 79, 43, 73, 421, 73, 181, 19, 157, 181, 3, 739, 421, 127, 103, 73, 571, 421, 109, 211, 1459, 103, 1693, 487, 829, 139, 1153, 439, 3067, 601, 199, 853, 421, 3541, 1069, 1279, 1297 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..1800

EXAMPLE

3*2^2-1=11 prime so a(1)=3 as 2 is prime(1).

3*2^3-1=23 prime so a(2)=3 as 3 is prime(2).

3*2^5-1=95 composite.

5*2^5-1=159 composite.

7*2^5-1=223 prime so a(3)=7 as 5 is prime(3).

MATHEMATICA

a249382[n_Integer] := Module[{q = 2}, While[! PrimeQ[Prime[q]*2^Prime[n] - 1], q++]; Prime[q]]; a249382/@Range[53] (* Michael De Vlieger, Nov 12 2014 *)

PROG

(PFGW & SCRIPT)

SCRIPT

DIM i

DIM j

DIM n, 0

OPENFILEOUT myf, a(n)

LABEL loop1

SET n, n+1

SET i, 1

LABEL loop2

SET i, i+1

SET j, p(i)

PRP j*2^p(n)-1

IF ISPRP THEN GOTO a

GOTO loop2

LABEL a

WRITE myf, j

GOTO loop1

(PARI) listp(nn) = {for (n=1, nn, k=2; while(!isprime(prime(k)*2^prime(n)-1), k++); print1(prime(k), ", "); ); } \\ Michel Marcus, Oct 27 2014

CROSSREFS

Cf. A249383, A249384.

Sequence in context: A076560 A096915 A249806 * A317929 A285387 A100803

Adjacent sequences:  A249379 A249380 A249381 * A249383 A249384 A249385

KEYWORD

nonn

AUTHOR

Pierre CAMI, Oct 27 2014

STATUS

approved

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Last modified March 30 22:55 EDT 2020. Contains 333132 sequences. (Running on oeis4.)