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A088739
Smallest semiprime divisor of n-th composite number.
6
4, 6, 4, 9, 10, 4, 14, 15, 4, 6, 4, 21, 22, 4, 25, 26, 9, 4, 6, 4, 33, 34, 35, 4, 38, 39, 4, 6, 4, 9, 46, 4, 49, 10, 51, 4, 6, 55, 4, 57, 58, 4, 62, 9, 4, 65, 6, 4, 69, 10, 4, 74, 15, 4, 77, 6, 4, 9, 82, 4, 85, 86, 87, 4, 6, 91, 4, 93, 94, 95, 4, 14, 9, 4, 6, 4, 15, 106, 4, 10, 111, 4
OFFSET
1,1
COMMENTS
This is to semiprimes A001358 as A052369 is to primes A000040. - Jonathan Vos Post, Jan 11 2011
MATHEMATICA
semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; f[n_] := Min@ Select[ Divisors@ n, semiPrimeQ] /. {\[Infinity] -> 0}; f /@ Rest@ Select[ Range@ 112, !PrimeQ@ # &]
Reap[Do[If[! PrimeQ[n], Sow[Select[Divisors[n], PrimeOmega[#] == 2 &][[1]]]], {n, 4, 1200}]][[2, 1]] (* Zak Seidov, Mar 18 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Oct 12 2003
STATUS
approved