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A217651 Primes of the form 2*n!!! - 1. 0
3, 5, 7, 19, 1759, 192684799, 14285134079, 145284339199, 509122178611199, 53165268316159999, 253515360530431999, 89312661819089868632723554303999999, 25863781053916181957690694149957243371519999999 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n !!! is a triple factorial number (see the definition in A007661).

The corresponding n are in A217650.

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

19 is in the sequence because n = 5 => 2*5 !!! - 1 = 2*10 - 1 = 19 is prime.

MAPLE

A:= n -> mul(k, k = select(k -> k mod 3 = n mod 3, [$1 .. n])): for p from 0 to 200 do:if type(2*A(p)-1, prime)=true then printf(`%d, `, 2*A(p)-1):else fi:od:

MATHEMATICA

multiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*multiFactorial[n - k, k]]];

Select[Table[2*multiFactorial[n, 3] - 1, {n, 0, 60}], PrimeQ]

CROSSREFS

Cf. A007661, A217650, A217648.

Sequence in context: A126144 A171643 A072002 * A163637 A228068 A182233

Adjacent sequences:  A217648 A217649 A217650 * A217652 A217653 A217654

KEYWORD

nonn

AUTHOR

Michel Lagneau, Oct 09 2012

STATUS

approved

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Last modified August 8 08:27 EDT 2020. Contains 336293 sequences. (Running on oeis4.)