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A221491
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Number of primes of the form k*n - k + n, 1 <= k <= n.
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3
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0, 1, 2, 2, 2, 2, 5, 2, 3, 3, 5, 3, 6, 4, 7, 6, 5, 4, 9, 2, 8, 7, 8, 4, 11, 5, 10, 8, 10, 4, 16, 3, 10, 10, 12, 9, 15, 4, 10, 11, 13, 6, 20, 7, 11, 10, 15, 8, 19, 6, 19, 13, 16, 5, 25, 10, 19, 10, 15, 9, 26, 7, 16, 13, 16, 13, 30, 9, 18, 14, 26, 10, 25, 10
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OFFSET
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1,3
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COMMENTS
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LINKS
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EXAMPLE
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Row 10 of A162610 = [19,28,37,46,55,64,73,82,91,100] containing three primes: [19,37,73], therefore a(10) = 3;
row 11 of A162610 = [21,31,41,51,61,71,81,91,101,111,121] containing five primes: [31,41,61,71,101], therefore a(11) = 5.
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MATHEMATICA
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a[n_] := Sum[Boole[PrimeQ[(k+1)(n-1)+1]], {k, 1, n}];
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PROG
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(Haskell)
a221491 n = sum [a010051' (k*n - k + n) | k <- [1..n]]
(PARI) a(n) = sum(k=1, n, isprime(k*n - k + n)); \\ Michel Marcus, Jan 26 2022
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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