Multiplication by 11 is easy ! To multiply a 2-digit number, add the two digits and place the sum in between! 25 * 11 = 275 31 * 11 = 341 57 * 11 = 627 <---- You need to carry the 1 !!! What about a 3-digit number? Can you figure out what is going on here? 253 * 11 = 2783 117 * 11 = 1287 532 * 11 = 5852 267 * 11 = 2937 If you want any help or if you want to comment on this, please feel free to E-Mail me (given below). How is 11 connected with Pascal Triangle..! Consider the triangle: ......1...... .....1..1..... ....1..2..1.... ..1..3..3..1... .1.4..6..4..1... ..................... (that continues in this fashion, where each entry is the sum of the 2 entries above it). Do you recognize the rows of this triangle? This is a quick way to generate the coefficients of (x+y)^n from algebra. And, better yet, you can use them as a quick way to calculate the powers of 11. (Since 11 = 10 + 1). 11, 121, 1331, .... are all powers of 11. Why dont you try 11^4 , 11^5, 11^6, etc....As a hint, I shall say that they are a bit harder, because you need to carry numbers.