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 A245715 Least number k > 0 such that n - k! is prime, or 0 if no such k exists. 3
 0, 0, 1, 1, 2, 1, 2, 1, 2, 0, 3, 1, 2, 1, 2, 0, 3, 1, 2, 1, 2, 0, 3, 1, 2, 4, 4, 0, 3, 1, 2, 1, 2, 0, 3, 0, 3, 1, 2, 0, 4, 1, 2, 1, 2, 0, 3, 1, 2, 0, 0, 0, 3, 1, 2, 0, 0, 0, 3, 1, 2, 1, 2, 0, 3, 0, 3, 1, 2, 0, 4, 1, 2, 1, 2, 0, 3, 0, 3, 1, 2, 0, 4, 1, 2, 0, 0, 0, 3, 1, 2, 0, 0, 0, 3, 0, 4, 1, 2, 0, 0, 1, 2, 1, 2, 0, 3, 1, 2, 1, 2, 0, 3, 1, 2, 0, 0, 0, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS a(n)! < n for all n. Thus a(n) = 0 is definite. LINKS Jens Kruse Andersen, Table of n, a(n) for n = 1..10000 EXAMPLE 11 - 1! = 10 is not prime. 11 - 2! = 9 is not prime. 11 - 3! = 5 is prime. Thus a(11) = 3. PROG (PARI) a(n)=for(k=1, n, if(ispseudoprime(n-k!), return(k))) vector(150, n, a(n)) CROSSREFS Sequence in context: A274820 A230583 A197366 * A337736 A047885 A072731 Adjacent sequences:  A245712 A245713 A245714 * A245716 A245717 A245718 KEYWORD nonn AUTHOR Derek Orr, Jul 30 2014 STATUS approved

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Last modified January 28 18:02 EST 2022. Contains 350657 sequences. (Running on oeis4.)