A166851 Numbers k such that reversal(k!+k) is prime.

1, 5, 37, 857, 2566

Offset

1,2

Comments

It's obvious that 1 is the only number k such that k!+k is prime.

There is no further term up to 5000.

There is no further term up to 25000. - Michael S. Branicky, Nov 14 2024

Links

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

Example

37!+37 = 13763753091226345046315979581580902400000037 and reversal(37!+37) =
73000000420908518597951364054362219035736731 is prime, so 37 is in the sequence.

Mathematica

reversal[n_]:=FromDigits[Reverse[IntegerDigits[n]]];
Do[If[PrimeQ[reversal[n!+n]], Print[n]], {n, 5000}]

Crossrefs

Sequence in context: A257952 A240186 A003213 * A090439 A089795 A081971

Adjacent sequences: A166848 A166849 A166850 * A166852 A166853 A166854

Keyword

base,hard,more,nonn

Author

Farideh Firoozbakht, Oct 22 2009

Status

approved