A303937 Numbers k such that k!-1 reversed is a prime.

3, 5, 19, 254, 266

Offset: 1

Author

Paolo Galliani, May 03 2018

Keywords

• nonn
• base
• more

Comments

If it exists, a(6) > 3000. - Jon E. Schoenfield, May 04 2018

If it exists, a(6) > 5703. - J.W.L. (Jan) Eerland, Aug 08 2022

If it exists, a(6) > 10142. - J.W.L. (Jan) Eerland, Aug 14 2022

If it exists, a(6) > 15000. - J.W.L. (Jan) Eerland, Oct 16 2022

If it exists, a(6) > 17506. - J.W.L. (Jan) Eerland, Nov 26 2022

If it exists, a(6) > 35000. - Michael S. Branicky, Dec 16 2024

Examples

			5 is in the sequence because 5!-1 reversed is 911, which is prime.
		

Crossrefs

Cf. A298702, A033312.

Programs

Mathematica

ParallelTable[If[PrimeQ[IntegerReverse[Factorial[k]-1]],k,Nothing],{k,1,5703}]//.{}->Nothing (* J.W.L. (Jan) Eerland, Aug 08 2022 *)

PARI

isok(n) = isprime(fromdigits(Vecrev(digits(n!-1))));