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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is to semiprimes A001358 as A052369 is to primes A000040. - Jonathan Vos Post, Jan 11 2011

LINKS

Zak Seidov, Table of n, a(n) for n = 1..1000

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

Cf. A088740, A002808, A001358.

Sequence in context: A054002 A010300 A113209 * A088740 A088738 A114595

Adjacent sequences:  A088736 A088737 A088738 * A088740 A088741 A088742

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 12 2003

STATUS

approved

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Last modified April 6 10:56 EDT 2020. Contains 333273 sequences. (Running on oeis4.)