The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A119739 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A119739

Numbers k such that 7^k + 3 is semiprime.
(history; published version)

#14 by Michel Marcus at Sun Feb 12 14:25:27 EST 2023

STATUS

reviewed

approved

#13 by Andrew Howroyd at Sun Feb 12 13:54:30 EST 2023

STATUS

proposed

reviewed

#12 by Michel Marcus at Sun Feb 12 13:25:03 EST 2023

STATUS

editing

proposed

#11 by Michel Marcus at Sun Feb 12 13:24:56 EST 2023

MATHEMATICA

Do[ If[ PrimeQ[(7^n + 3)/2], Print@n], {n, 1, 11501, 2}] (* Robert G. Wilson v , Jun 14 2006 *)

STATUS

proposed

editing

#10 by Tyler Busby at Sun Feb 12 12:45:13 EST 2023

STATUS

editing

proposed

#9 by Tyler Busby at Sun Feb 12 12:45:02 EST 2023

DATA

1, 3, 31, 47, 83, 1255, 39015

COMMENTS

a(8) > 120000. - Tyler Busby, Feb 12 2023

EXTENSIONS

a(7) from Tyler Busby, Feb 12 2023

STATUS

approved

editing

#8 by Susanna Cuyler at Wed Mar 04 21:21:23 EST 2020

STATUS

proposed

approved

#7 by Jinyuan Wang at Wed Mar 04 21:14:23 EST 2020

STATUS

editing

proposed

#6 by Jinyuan Wang at Wed Mar 04 21:14:14 EST 2020

NAME

Numbers n k such that 7^nk + 3 is semiprime.

COMMENTS

Or (7^nk + 3)/2 is prime.

a(7) > 18000. - Jinyuan Wang, Mar 04 2020

EXAMPLE

7^1 + 3 = 19 = 2*5,

7^3 + 3 = 346 = 2*173,

7^31 + 3 = 2*78887691017422903307521373,

7^47 + 3 = 2*2621669158378151817230729359430975727773,

7^83 + 3 = 2*6951960974910262341699296037696359556850100616048572362472005937832173.

PROG

(PARI) is(k) = ispseudoprime((7^k+3)/2); \\ Jinyuan Wang, Mar 04 2020

KEYWORD

more,nonn,more,less

STATUS

approved

editing

#5 by N. J. A. Sloane at Thu Oct 31 12:17:39 EDT 2013

MATHEMATICA

Do[ If[ PrimeQ[(7^n + 3)/2], Print@n], {n, 1, 11501, 2}] (* _Robert G. Wilson v _ *)

Discussion

Thu Oct 31

12:17

OEIS Server: https://oeis.org/edit/global/2036