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 A126867 Largest even semiprime <= n^2. 1

%I

%S 4,6,14,22,34,46,62,74,94,118,142,166,194,218,254,278,314,358,398,422,

%T 482,526,566,622,674,718,778,838,898,958,1018,1082,1154,1214,1294,

%U 1366,1438,1514,1594,1678,1762,1838,1934,2018,2102,2206,2302,2386,2498,2594

%N Largest even semiprime <= n^2.

%H Robert Israel, <a href="/A126867/b126867.txt">Table of n, a(n) for n = 2..10000</a>

%F a(n) = max( A001358(i): A001358(i)<= A000290(n), A001358(i)= 0 mod 2). - _R. J. Mathar_, Mar 17 2007

%p isA001358 := proc(n) if numtheory[bigomega](n)=2 then true; else false; fi; end: A126867 := proc(n) local a; a := n^2; while not isA001358(a) or a mod 2 <> 0 do a := a-1; od; RETURN(a); end: for n from 2 to 90 do printf("%d, ", A126867(n)); od; # _R. J. Mathar_, Mar 17 2007

%p # Alternative:

%p f:= n -> 2*prevprime(ceil(n^2/2)): f(2):= 4:

%p map(f, [\$2..100]); # _Robert Israel_, Jun 20 2019

%t f[n_] := 2Prime[PrimePi[n^2/2]];Table[f[n], {n, 2, 51}] (* _Ray Chandler_, Mar 17 2007 *)

%K easy,nonn

%O 2,1

%A _Giovanni Teofilatto_, Mar 16 2007

%E Extended by _Ray Chandler_, _Robert G. Wilson v_ and _R. J. Mathar_, Mar 17 2007

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Last modified May 7 10:32 EDT 2021. Contains 343650 sequences. (Running on oeis4.)