OFFSET
1,4
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
The prime factors of 250 are {2,5,5,5}, with right half (exclusive) {5,5}, with product 25, so a(250) = 25.
MAPLE
f:= proc(n) local F;
F:= ifactors(n)[2];
F:= sort(map(t -> t[1]$t[2], F));
convert(F[ceil(nops(F)/2)+1 ..-1], `*`)
end proc:
f(1):= 0:
map(f, [$1..100]); # Robert Israel, Aug 12 2024
MATHEMATICA
Table[If[n==1, 0, Times@@Take[Join@@ConstantArray@@@FactorInteger[n], -Floor[PrimeOmega[n]/2]]], {n, 100}]
CROSSREFS
Positions of 1's are A000040.
Positions of first appearances are A123666.
The left inclusive version A347043.
The inclusive version is A347044.
The left version is A361200.
A000005 counts divisors.
A001221 counts distinct prime factors.
A006530 gives greatest prime factor.
First for prime indices, second for partitions, third for prime factors:
KEYWORD
nonn,look
AUTHOR
Gus Wiseman, Mar 10 2023
STATUS
approved