Ind. Code § 29-2-12-4

Sec. 4. The portion of the federal estate tax to be paid by each person, heir, or beneficiary of a decedent's estate shall be determined by dividing the value of the property received by the person, heir, or beneficiary, which is included in the net taxable estate, by the amount of the net taxable estate, and multiplying the result by the amount of the total federal estate tax paid.