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A087461
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Arithmetic mean of n-th and 2n-th primes.
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4
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5, 9, 13, 20, 25, 30, 36, 42, 50, 55, 63, 71, 75, 80, 92, 99, 106, 115, 122, 127, 136, 141, 156, 163, 170, 177, 185, 190, 197, 210, 221, 227, 238, 249, 255, 265, 273, 282, 291, 300, 307, 317, 325, 330, 339, 351, 363, 374, 385, 395, 404, 409, 422, 429, 438, 444
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OFFSET
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2,1
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COMMENTS
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A rather sparse subset are primes: 5, 13, 71, = a(2), a(4), a(13).
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LINKS
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FORMULA
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a(n) = (n-th prime + 2n-th prime)/2
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EXAMPLE
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Series begins with 2nd prime, 3 and 4th prime, 7. Then (3 + 7)/2 = 5.
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MATHEMATICA
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Table[Mean[{Prime[n], Prime[2n]}], {n, 2, 60}] (* Harvey P. Dale, May 25 2011 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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