Which sutra is not useful for multiplication:A.     Ekadhikena poorvenaB.     Ekanyunen poorvenaC.     Urdhav tiryagbhyamamD.     Nikhilam

To determine which sutra is not useful for multiplication, we need to analyze each option:

A. Ekadhikena poorvena: This sutra is useful for multiplication as it means "one more than the previous one." It is commonly used to multiply numbers.

B. Ekanyunen poorvena: This sutra is also useful for multiplication as it means "one less than the previous one." It is often used in Vedic mathematics for multiplication.

C. Urdhav tiryagbhyamam: This sutra is not specifically related to multiplication. It means "vertically and crosswise." It is used for various mathematical operations, but not specifically for multiplication.

D. Nikhilam: This sutra is useful for multiplication as it means "all from 9 and the last from 10." It is commonly used to multiply numbers.

Based on the analysis, the sutra that is not useful for multiplication is option C. Urdhav tiryagbhyamam.