OFFSET
1,4
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
The prime factors of 250 are {2,5,5,5}, with left half (exclusive) {2,5}, with product 10, so a(250) = 10.
MATHEMATICA
Table[If[n==1, 0, Times@@Take[Join@@ConstantArray@@@FactorInteger[n], Floor[PrimeOmega[n]/2]]], {n, 100}]
a[n_] := Module[{p = Flatten[Table[#[[1]], {#[[2]]}] & /@ FactorInteger[n]]}, Times @@ p[[1 ;; Floor[Length[p]/2]]]]; a[1] = 0; Array[a, 100] (* Amiram Eldar, Nov 02 2024 *)
CROSSREFS
Positions of 1's are A000040.
Positions of 2's are A037143.
The inclusive version is A347043.
The right inclusive version A347044.
The right version is A361201.
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,changed
AUTHOR
Gus Wiseman, Mar 10 2023
STATUS
approved