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 A245756 Least number k such that (k! + n)/k is prime, or 0 if no such k exists. 4
 1, 1, 3, 1, 0, 1, 0, 2, 3, 1, 0, 1, 0, 0, 3, 1, 0, 1, 0, 2, 0, 1, 0, 2, 5, 0, 3, 1, 0, 1, 0, 2, 3, 0, 5, 1, 0, 38, 0, 1, 0, 1, 0, 2, 3, 1, 0, 0, 7, 0, 3, 1, 0, 0, 0, 2, 0, 1, 0, 1, 0, 0, 3, 0, 5, 1, 0, 4, 0, 1, 0, 1, 0, 74, 0, 0, 0, 1, 0, 2, 3, 1, 0, 2, 5, 0, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS If a(n) = n, then n is in A090660. a(n) <= n for all n. a(n) = 1 if and only if n + 1 is prime. LINKS Jens Kruse Andersen, Table of n, a(n) for n = 1..1000 EXAMPLE (1! + 3)/1 = 4 is not prime. (2! + 3)/2 = 5/2 is not prime. (3! + 3)/3 = 3 is prime. Thus a(3) = 3. PROG (PARI) a(n)=for(k=1, n, s=(k!+n)/k; if(floor(s)==s, if(ispseudoprime(s), return(k)))) n=1; while(n<150, print1(a(n), ", "); n++) CROSSREFS Cf. A090660. Sequence in context: A111700 A233316 A060096 * A322512 A152892 A193002 Adjacent sequences:  A245753 A245754 A245755 * A245757 A245758 A245759 KEYWORD nonn AUTHOR Derek Orr, Jul 31 2014 EXTENSIONS Corrected by Jens Kruse Andersen, Aug 03 2014 STATUS approved

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Last modified May 29 10:41 EDT 2020. Contains 334699 sequences. (Running on oeis4.)