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A328903
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Number of primes that are a concatenation of two positive integers whose sum is n.
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4
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0, 0, 1, 0, 2, 2, 0, 2, 3, 0, 3, 4, 0, 3, 5, 0, 4, 2, 0, 6, 5, 0, 4, 5, 0, 6, 7, 0, 6, 9, 0, 6, 8, 0, 9, 8, 0, 7, 7, 0, 9, 10, 0, 11, 2, 0, 12, 12, 0, 10, 11, 0, 11, 14, 0, 3, 10, 0, 10, 12, 0, 16, 12, 0, 16, 14, 0, 14, 19, 0, 13, 17, 0, 12, 16, 0, 15, 2, 0
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OFFSET
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0,5
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COMMENTS
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First n > 1 with n != 0 (mod 3) and a(n) = 0 is n = 4477. - Alois P. Heinz, Oct 30 2019
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LINKS
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FORMULA
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EXAMPLE
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1(-), 2(11), 3(-), 4(13, 31), 5(23, 41), 6(-), 7(43, 61), 8(17, 53, 71), 9(-), 10(19, 37, 73), 11(29, 47, 83, 101), 12(-), 13(67, 103, 211), ...
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MAPLE
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a:= proc(n) option remember; `if`(irem(n, 3)=0, 0, add(
`if`(isprime(parse(cat(i, n-i))), 1, 0), i=1..n-1))
end:
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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