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A135726
Primes of the form n!!!-1 = A007661(n)-1, n>0.
3
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
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
KEYWORD
nonn
AUTHOR
M. F. Hasler, Nov 26 2007
STATUS
approved