A166850 Numbers n such that reversal(n!-n) is prime.

3, 4, 56, 128, 197, 331

Offset

1,1

Comments

It's obvious that there is no number n such that n!-n is prime.

There is no further term up to 5000.

Links

Table of n, a(n) for n=1..6.

Example

56!-56=
710998587804863451854045647463724949736497978881168458687447039999999999944
and reversal(56!-56)=
449999999999930744786854861188879794637949427364746540458154368408785899017
is prime so 56 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: A114694 A272337 A132678 * A317856 A331725 A067093

Adjacent sequences: A166847 A166848 A166849 * A166851 A166852 A166853

Keyword

base,hard,more,nonn

Author

Farideh Firoozbakht, Oct 22 2009

Status

approved