login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A084438 Positive integers n such that n!!!-1 = A007661(n)-1 is prime. 59
3, 4, 6, 8, 20, 26, 36, 50, 60, 114, 135, 138, 248, 315, 351, 429, 642, 5505, 8793, 12086, 13580, 23109, 34626, 34706, 56282, 57675, 58298 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The search for multifactorial primes started by Ray Ballinger is now continued by a team of volunteers on the website of Ken Davis (see link).

LINKS

Table of n, a(n) for n=1..27.

Ken Davis, Status of Search for Multifactorial Primes.

Ken Davis, Results for n!3-1.

ProthSearch.net (on web.archive.org), n3minus.txt

EXAMPLE

a(4)=8 since 8!!!-1 = 8*5*2-1 = 79 is the 4th prime of that form.

26!!!-1 = 2504902399 is prime.

PROG

(PARI) A007661(n) = prod(i=1, (n-1)\3, n-=3, n+!n) /* newline */ for(n=1, 999, if(isprime(A007661(n)-1), print1(n", "))) - M. F. Hasler, Nov 26 2007

CROSSREFS

Cf. A007661, A135726, A037082, A037083.

Sequence in context: A134580 A007749 A063506 * A186700 A028987 A284615

Adjacent sequences:  A084435 A084436 A084437 * A084439 A084440 A084441

KEYWORD

hard,nonn

AUTHOR

Hugo Pfoertner, Jun 25 2003

EXTENSIONS

Missing 26 inserted by M. F. Hasler, Nov 26 2007

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

Edited by N. J. A. Sloane, Feb 11 2009 at the suggestion of M. F. Hasler

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 14 09:20 EST 2018. Contains 318091 sequences. (Running on oeis4.)