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A304874
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Greatest prime p1 < p2 such that n^2 = (p1 + p2)/2 and p2 is prime.
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5
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3, 7, 13, 19, 31, 37, 61, 79, 97, 103, 139, 157, 193, 223, 241, 271, 317, 349, 379, 439, 421, 487, 521, 619, 661, 719, 757, 829, 881, 883, 1009, 1087, 1063, 1213, 1291, 1291, 1429, 1511, 1579, 1669, 1741, 1831, 1879
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OFFSET
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2,1
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COMMENTS
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Each square > 1 can be written as the average of 2 primes p1 < p2. a(n) gives the greatest prime p1 such that n^2 = (p1 + p2) / 2. The corresponding p2 is provided in A304875.
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 3 because 2^2 = 4 = (3 + 5)/2,
a(7) = 37 because 7^2 = 49 = (37 + 61)/2 and none of the primes p1 = 41, 43 or 47 leads to a prime p2.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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