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A265201 Numbers n such that n!!! - 3^10 is prime, where n!3 = n!!! is a triple factorial number (A007661).. 2
19, 20, 22, 26, 41, 55, 56, 152, 155, 316, 347, 383, 500, 556, 646, 656, 748, 976, 1433, 2213, 2680, 2911, 3373, 4799, 4964, 7189, 8798, 9871, 14069, 14627, 16657, 20230, 24137, 24430, 28331, 36313, 41522, 43031, 46072, 47719 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes are 1047511, 4129751, 24285271, 2504843351, 126757680265156951, ... .

a(41) > 50000.

LINKS

Table of n, a(n) for n=1..40.

Henri & Renaud Lifchitz, PRP Records. Search for n!3-59049.

Joe McLean, Interesting Sources of Probable Primes

EXAMPLE

19!3 - 3^10 = 19*16*13*10*7*4*1 - 59049 = 1047511 is prime, so 19 is in the sequence.

MATHEMATICA

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

Select[Range[17, 50000], PrimeQ[MultiFactorial[#, 3] - 3^10] &]

PROG

(PARI) tf(n) = prod(i=0, (n-1)\3, n-3*i);

for(n=1, 1e4, if(ispseudoprime(tf(n) - 3^10), print1(n , ", "))) \\ Altug Alkan, Dec 04 2015

CROSSREFS

Cf. A006882, A007749, A094144, A123910, A258452, A258616, A262772, A261145.

Sequence in context: A289469 A093680 A007640 * A274340 A241849 A054304

Adjacent sequences:  A265198 A265199 A265200 * A265202 A265203 A265204

KEYWORD

hard,more,nonn

AUTHOR

Robert Price, Dec 04 2015

STATUS

approved

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Last modified July 31 18:30 EDT 2021. Contains 346376 sequences. (Running on oeis4.)