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a(n) is the largest prime smaller than sqrt(prime(n)*prime(n+6)).
2

%I #10 Jul 03 2019 13:15:30

%S 5,7,7,13,17,19,23,23,31,37,41,47,47,53,53,61,67,73,79,83,83,89,89,97,

%T 109,113,113,113,127,127,139,139,151,151,163,163,173,173,181,181,193,

%U 199,199,199,211,211,223,233,241,241,241,251,257,263,269

%N a(n) is the largest prime smaller than sqrt(prime(n)*prime(n+6)).

%H Robert Israel, <a href="/A126992/b126992.txt">Table of n, a(n) for n = 1..10000</a>

%p f:= n -> prevprime(ceil(sqrt(ithprime(n)*ithprime(n+6)))):

%p map(f, [$1..100]); # _Robert Israel_, Jun 21 2018

%t Table[Prime[PrimePi[Sqrt[Prime[n]*Prime[n + 6]]]], {n, 1, 55}]

%t Table[NextPrime[Sqrt[Prime[n]Prime[n+6]],-1],{n,60}] (* _Harvey P. Dale_, Jul 03 2019 *)

%K nonn

%O 1,1

%A _Artur Jasinski_, Jan 01 2007

%E Edited by _Stefan Steinerberger_, Jul 31 2007