A135726 Primes of the form n!!!-1 = A007661(n)-1, n>0.

2, 3, 17, 79, 4188799, 2504902399, 254561089305599, 13106744139423334399999, 8483004771271882804592639999, 706526001186582385898210420541078864497278132689882316799999999

Offset

1,1

Comments

Sequence A084438 gives the easier-to-read n-values.

All terms greater than a(3) seem to end in the digit 9, or many 9 digits. a(17) ends with 51 9 digits. - Harvey P. Dale, Nov 28 2019

Links

Harvey P. Dale, Table of n, a(n) for n = 1..17

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) = 79 = 8x5x2-1 = 8!!!-1 is the 4th prime of that form.

Mathematica

Select[Table[Times@@Range[n, 1, -3], {n, 150}]-1, PrimeQ] (* Harvey P. Dale, Nov 28 2019 *)

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(A007661(n)-1, ", ")))

Crossrefs

Cf. A007661, A084438, A037082, A037083.

Sequence in context: A342547 A245799 A056794 * A164816 A259535 A328340

Adjacent sequences: A135723 A135724 A135725 * A135727 A135728 A135729

Keyword

nonn

Author

M. F. Hasler, Nov 26 2007

Status

approved