FactorTermsList

FactorTermsList[poly] gives a list where the first element is the overall numerical factor and the second is the polynomial with the factor removed.

Examples

Get numerical factor and remainder:

FactorTermsList[6x + 12y]
(* {6, x + 2 y} *)

With multiple variables:

FactorTermsList[a b x + a b y, {x, y}]
(* {1, a b, x + y} *)

Please visit the official Wolfram Language Reference for more details.