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A217651
Primes of the form 2*k!!! - 1.
0
3, 5, 7, 19, 1759, 192684799, 14285134079, 145284339199, 509122178611199, 53165268316159999, 253515360530431999, 89312661819089868632723554303999999, 25863781053916181957690694149957243371519999999
OFFSET
1,1
COMMENTS
k!!! is a triple factorial number (see the definition in A007661).
The corresponding k are in A217650.
EXAMPLE
19 is in the sequence because k = 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
KEYWORD
nonn
AUTHOR
Michel Lagneau, Oct 09 2012
STATUS
approved