login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A264867 Numbers n such that n!3 + 3^8 is prime, where n!3 = n!!! is a triple factorial number (A007661). 1
2, 5, 10, 26, 34, 35, 37, 59, 68, 76, 104, 106, 188, 193, 242, 278, 287, 290, 572, 772, 773, 1304, 2384, 2716, 3715, 4562, 6706, 11489, 11711, 21602, 24295, 24775, 27224, 29935, 37856 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes are 6563, 6571, 6841, 2504908961, 17961239302561, 81359229958561, 664565853958561, ...

Terms > 68 correspond to probable primes.

a(36) > 50000.

LINKS

Table of n, a(n) for n=1..35.

Henri & Renaud Lifchitz, PRP Records. Search for n!3+3^8

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

EXAMPLE

10!3 + 3^4 = 10*7*4*1 + 6561 = 6841 is prime, so 10 is in the sequence.

MATHEMATICA

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

Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 3] + 3^8] &]

PROG

(PARI) is(n)=ispseudoprime(n!!! + 3^8) \\ Anders Hellström, Nov 27 2015

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

for(n=1, 1e4, if(ispseudoprime(tf(n) + 3^8), print1(n , ", "))) \\  Altug Alkan, Dec 03 2015

CROSSREFS

Cf. A007661, A037082, A084438, A243078.

Sequence in context: A297860 A002094 A212709 * A115725 A305577 A196630

Adjacent sequences:  A264864 A264865 A264866 * A264868 A264869 A264870

KEYWORD

nonn,more

AUTHOR

Robert Price, Nov 26 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 20 16:30 EDT 2019. Contains 327242 sequences. (Running on oeis4.)