A243078 Numbers k such that k!3 - 3^2 is prime, where k!3 = k!!! is a triple factorial number (A007661).

7, 8, 10, 13, 16, 17, 20, 23, 28, 29, 32, 43, 46, 47, 53, 56, 59, 61, 76, 95, 107, 139, 148, 218, 349, 764, 1009, 1130, 1183, 1429, 1516, 2072, 2471, 4937, 10204, 13993, 16249, 18166, 25733, 29033, 40090

Offset: 1

Author

Robert Price, May 30 2014

Keywords

• nonn
• more

Comments

a(42) > 50000.

k=2 and k=4 produce values (-7 and -5) whose absolute value is a prime.

Terms > 2000 correspond to probable primes.

Examples

			17!3 - 3^2 = 17*14*11*8*5*2 - 9 = 209431 is prime, so 17 is in the sequence. - _Jens Kruse Andersen_, Aug 20 2014
		

Links

• Henri & Renaud Lifchitz, PRP Records. Search for n!3-9.
• OpenPFGW Project, Primality Tester

Crossrefs

Cf. A007661, A037082, A084438, A123910, A242994.

Programs

Mathematica

MultiFactorial[n_,k_]:=If[n<1,1,If[n
				

Extensions

a(41) from Robert Price, Sep 19 2014