A088740 Greatest semiprime divisor of n-th composite number.

4, 6, 4, 9, 10, 6, 14, 15, 4, 9, 10, 21, 22, 6, 25, 26, 9, 14, 15, 4, 33, 34, 35, 9, 38, 39, 10, 21, 22, 15, 46, 6, 49, 25, 51, 26, 9, 55, 14, 57, 58, 15, 62, 21, 4, 65, 33, 34, 69, 35, 9, 74, 25, 38, 77, 39, 10, 9, 82, 21, 85, 86, 87, 22, 15, 91, 46, 93, 94, 95, 6, 49, 33, 25

Offset: 1

Author

Reinhard Zumkeller, Oct 12 2003

Keywords

• nonn

Links

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

Crossrefs

Cf. A088739, A002808, A001358.

Programs

Mathematica

Reap[Do[If[! PrimeQ[n], fl = Flatten[Table[#[[1]], {#[[2]]}] & /@ FactorInteger[n]]; Sow[fl[[-1]]*fl[[-2]]]], {n, 4, 1200}]][[2, 1]]; (* Zak Seidov, Mar 18 2013 *)
gsd[n_]:=Max[Select[Divisors[n],PrimeOmega[#]==2&]]; gsd/@Select[Range[ 200],CompositeQ] (* Harvey P. Dale, May 08 2022 *)