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

1,1

Links

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

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 *)

Crossrefs

Cf. A088739, A002808, A001358.

Sequence in context: A367731 A367096 A088739 * A088738 A114595 A256415

Adjacent sequences: A088737 A088738 A088739 * A088741 A088742 A088743

Keyword

nonn

Author

Reinhard Zumkeller, Oct 12 2003

Status

approved