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A083382
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Write the numbers from 1 to n^2 consecutively in n rows of length n; a(n) = minimal number of primes in a row.
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12
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0, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 2, 3, 3, 2, 2, 3, 3, 3, 3, 3, 2, 2, 2, 2, 3, 4, 3, 3, 4, 3, 3, 4, 3, 3, 4, 4, 4, 3, 3, 4, 5, 4, 3, 4, 5, 4, 5, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 7, 6, 4, 5, 6, 6, 5, 6, 6, 6, 6, 6, 7, 7, 6, 6, 6, 7, 7, 7, 7, 6, 6, 7, 7, 7
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OFFSET
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1,9
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COMMENTS
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Conjectured by Schinzel (Hypothesis H2) to be always positive for n > 1.
The conjecture has been verified for n = prime < 790000 by Aguilar.
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REFERENCES
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P. Ribenboim, The New Book of Prime Number Records, Chapter 6.
P. Ribenboim, The Little Book Of Big Primes, Springer-Verlag, NY 1991, page 185.
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LINKS
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EXAMPLE
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For n = 3 the array is
1 2 3 (2 primes)
4 5 6 (1 prime)
7 8 9 (1 prime)
so a(3) = 1
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MAPLE
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A083382 := proc(n) local t1, t2, at; t1 := n; at := 0; for i from 1 to n do t2 := 0; for j from 1 to n do at := at+1; if isprime(at) then t2 := t2+1; fi; od; if t2 < t1 then t1 := t2; fi; od; t1; end;
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MATHEMATICA
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Table[minP=n; Do[s=0; Do[If[PrimeQ[c+(r-1)*n], s++ ], {c, n}]; minP=Min[s, minP], {r, n}]; minP, {n, 100}]
Table[Min[Count[#, _?PrimeQ]&/@Partition[Range[n^2], n]], {n, 110}] (* Harvey P. Dale, May 29 2013 *)
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PROG
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(Haskell)
a083382 n = f n n a010051_list where
f m 0 _ = m
f m k chips = f (min m $ sum chin) (k - 1) chips' where
(chin, chips') = splitAt n chips
(PARI) A083382(n) = { my(m=-1); for(i=0, n-1, my(s=sum(j=(i*n), ((i+1)*n)-1, isprime(1+j))); if((m<0) || (s < m), m = s)); (m); }; \\ Antti Karttunen, Jan 01 2019
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CROSSREFS
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A084927 generalizes this to three dimensions.
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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