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

3, 5, 19, 254, 266

Offset

1,1

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

Links

Table of n, a(n) for n=1..5.

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A298702, A033312.

Sequence in context: A201108 A291920 A172058 * A062577 A144743 A171862

Adjacent sequences: A303934 A303935 A303936 * A303938 A303939 A303940

Keyword

nonn,base,more

Author

Paolo Galliani, May 03 2018

Status

approved