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A126867 Largest even semiprime <= n^2. 1
4, 6, 14, 22, 34, 46, 62, 74, 94, 118, 142, 166, 194, 218, 254, 278, 314, 358, 398, 422, 482, 526, 566, 622, 674, 718, 778, 838, 898, 958, 1018, 1082, 1154, 1214, 1294, 1366, 1438, 1514, 1594, 1678, 1762, 1838, 1934, 2018, 2102, 2206, 2302, 2386, 2498, 2594 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Robert Israel, Table of n, a(n) for n = 2..10000

FORMULA

a(n) = max( A001358(i): A001358(i)<= A000290(n), A001358(i)= 0 mod 2). - R. J. Mathar, Mar 17 2007

MAPLE

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

# Alternative:

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

map(f, [$2..100]); # Robert Israel, Jun 20 2019

MATHEMATICA

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

CROSSREFS

Sequence in context: A122555 A210632 A097271 * A027632 A175722 A200186

Adjacent sequences:  A126864 A126865 A126866 * A126868 A126869 A126870

KEYWORD

easy,nonn

AUTHOR

Giovanni Teofilatto, Mar 16 2007

EXTENSIONS

Extended by Ray Chandler, Robert G. Wilson v and R. J. Mathar, Mar 17 2007

STATUS

approved

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Last modified May 26 15:50 EDT 2020. Contains 334626 sequences. (Running on oeis4.)