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%I #30 Aug 24 2021 06:28:38
%S 256,5392,116288,2210465,28444929,255528577,4009404505,153081728914,
%T 5171603025026,62036152111810,699273704703624,25869244015854483,
%U 1361620781025221899,22882871550589429987,317257878688421267438,11004311280566297309676,258894081066969988746661
%N a(n) = Sum_{j=1..n} c(j)^c(n+1-j) where c(k) is the k-th composite number.
%C For n smaller than 100, a(n) can be approximated by exp(0.0075*n^2 + 3.0857*n - 0.166).
%H Vincenzo Librandi, <a href="/A196152/b196152.txt">Table of n, a(n) for n = 1..200</a>
%F a(n) = Sum_{j=1..n} A002808(j)^A002808(n+1-j).
%e For n = 4, a(4) = 4^9 + 6^8 + 8^6 + 9^4 = 2210465.
%t Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1&, n]; Table[Sum[Composite[j]^Composite[i+1-j],{j,i}],{i,10}]
%o (PARI) iscomposite(n) = if (n==1, 0, !isprime(n));
%o 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
%Y Cf. A002808.
%K nonn
%O 1,1
%A _Josh Kirklin_, Sep 28 2011