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A196152
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a(n) = Sum_{j=1..n} c(j)^c(n+1-j) where c(k) is the k-th composite number.
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1
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256, 5392, 116288, 2210465, 28444929, 255528577, 4009404505, 153081728914, 5171603025026, 62036152111810, 699273704703624, 25869244015854483, 1361620781025221899, 22882871550589429987, 317257878688421267438, 11004311280566297309676, 258894081066969988746661
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OFFSET
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1,1
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COMMENTS
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For n smaller than 100, a(n) can be approximated by exp(0.0075*n^2 + 3.0857*n - 0.166).
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LINKS
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FORMULA
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EXAMPLE
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For n = 4, a(4) = 4^9 + 6^8 + 8^6 + 9^4 = 2210465.
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MATHEMATICA
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Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1&, n]; Table[Sum[Composite[j]^Composite[i+1-j], {j, i}], {i, 10}]
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PROG
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(PARI) iscomposite(n) = if (n==1, 0, !isprime(n));
a(n) = {vc = []; ic = 1; while (#vc != n, if (iscomposite(ic), vc = concat(vc, ic)); ic++); sum(i=1, n, vc[i]^vc[n+1-i]); } \\ Michel Marcus, Aug 06 2014
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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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