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 A212595 Let f(n) = 2n-7. Difference between f(n) and the nearest prime <  f(n). 1
 2, 2, 4, 2, 2, 4, 2, 4, 6, 2, 2, 4, 6, 2, 4, 2, 2, 4, 2, 4, 6, 2, 4, 6, 2, 2, 4, 6, 2, 4, 2, 2, 4, 6, 2, 4, 2, 4, 6, 2, 4, 6, 8, 2, 4, 2, 2, 4, 2, 2, 4, 2, 4, 6, 8, 10, 12, 14, 2, 4, 2, 4, 6, 2, 2, 4, 6, 8, 10, 2, 2, 4, 6, 2, 4, 6, 2, 4, 2, 4, 6, 2, 4, 6, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 10,1 COMMENTS Itâ€™s known that there is always a prime between n and 2n - 7 for all n > = 10. LINKS Michel Lagneau, Table of n, a(n) for n = 10..10000 Peter Vandendriessche and Hojoo Lee, Problems in elementary number theory, Problem E37 EXAMPLE a(12) = 4 because 2*12-7 = 17, and the nearest prime p < 17 such that 12 < p < 17 is p = 13. Hence a(12) = 17 - 13 = 4. MAPLE with(numtheory):for n from 10 to 100 do:x:=2*n-7:i:=0:for p from x-1 by -1 to n+1 while(i=0) do:if type(p, prime)=true then i:=1:printf(`%d, `, x-p):else fi:od:od: CROSSREFS Sequence in context: A247257 A069177 A077659 * A087692 A093621 A242734 Adjacent sequences:  A212592 A212593 A212594 * A212596 A212597 A212598 KEYWORD nonn AUTHOR Michel Lagneau, May 22 2012 STATUS approved

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Last modified August 17 22:32 EDT 2018. Contains 313817 sequences. (Running on oeis4.)