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A166850 Numbers n such that reversal(n!-n) is prime. 0
3, 4, 56, 128, 197, 331 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 6 16:03 EDT 2021. Contains 343586 sequences. (Running on oeis4.)