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A084438 Positive integers n such that n!!!-1 = A007661(n)-1 is prime. 24
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 A186709

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

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Last modified March 27 12:14 EDT 2017. Contains 284176 sequences.