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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 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.)