# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a196152 Showing 1-1 of 1 %I A196152 #30 Aug 24 2021 06:28:38 %S A196152 256,5392,116288,2210465,28444929,255528577,4009404505,153081728914, %T A196152 5171603025026,62036152111810,699273704703624,25869244015854483, %U A196152 1361620781025221899,22882871550589429987,317257878688421267438,11004311280566297309676,258894081066969988746661 %N A196152 a(n) = Sum_{j=1..n} c(j)^c(n+1-j) where c(k) is the k-th composite number. %C A196152 For n smaller than 100, a(n) can be approximated by exp(0.0075*n^2 + 3.0857*n - 0.166). %H A196152 Vincenzo Librandi, Table of n, a(n) for n = 1..200 %F A196152 a(n) = Sum_{j=1..n} A002808(j)^A002808(n+1-j). %e A196152 For n = 4, a(4) = 4^9 + 6^8 + 8^6 + 9^4 = 2210465. %t A196152 Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1&, n]; Table[Sum[Composite[j]^Composite[i+1-j],{j,i}],{i,10}] %o A196152 (PARI) iscomposite(n) = if (n==1, 0, !isprime(n)); %o A196152 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 A196152 Cf. A002808. %K A196152 nonn %O A196152 1,1 %A A196152 _Josh Kirklin_, Sep 28 2011 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE