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A341982
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Number of ways to write n as an ordered sum of 2 primes (counting 1 as a prime).
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9
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1, 2, 3, 2, 3, 2, 4, 2, 3, 0, 4, 2, 5, 2, 4, 0, 6, 2, 6, 2, 5, 0, 8, 2, 5, 0, 4, 0, 8, 2, 6, 2, 7, 0, 8, 0, 5, 2, 6, 0, 10, 2, 8, 2, 7, 0, 12, 2, 8, 0, 6, 0, 12, 2, 6, 0, 7, 0, 14, 2, 7, 2, 10, 0, 12, 0, 6, 2, 10, 0, 14, 2, 11, 2, 10, 0, 14, 0, 10, 2, 9, 0, 18, 2, 9, 0, 8
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OFFSET
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2,2
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LINKS
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FORMULA
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G.f.: ( x + Sum_{k>=1} x^prime(k) )^2.
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MAPLE
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b:= proc(n) option remember; series(`if`(n=0, 1, x*add(
`if`(j=1 or isprime(j), b(n-j), 0), j=1..n)), x, 3)
end:
a:= n-> coeff(b(n), x, 2):
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MATHEMATICA
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nmax = 88; CoefficientList[Series[(x + Sum[x^Prime[k], {k, 1, nmax}])^2, {x, 0, nmax}], x] // Drop[#, 2] &
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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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