Sunday 17 December 2017

Blog Post # 98: The curious case of two six digit squares

Consider these two squares - 531441 and 254016

On the face of it, they appear like any other normal square. Let's look at some surprising facts

For starters 531441 is 729 * 729 and 254016 is 504 * 504 - Nothing unique as of now

a) Now look at the last 3 digits of both squares - 441 and 016 and both are perfect squares

b) Last digit of the square roots (729 and 504) - 9 and 4 and both are perfect squares

c) Difference between the square roots (729 and 504) is a perfect square again

d) 729 by itself is a perfect square as well as a cube

e) 504 is a unique number as it is the lowest three digit to have all factors from 1 to 9 except 5 (Once we multiple this number by 5 we get 2520 which is the smallest 4 digit number to have factors from 1 to 10)

f) Now dissect the original squares as following - 53 + 14 + 41 which gives 108 while 25 +40 + 16 gives 81 (108 and 81 are successive multiples of 27 which in turn is square root of 729!)

g) Multiple the non zero digits of both squares - 5*3*1*4*4*1 = 240, 2*5*4*1*6 = 240 again!

h) Prefix 1 to the square root of 531441 (which is 729) and we get the famous Ramanujan Number 1729. Now subtract the other square root 504 from 1729 and you get a perfect square 1225!

i) Suffix 1 to the square root of 254016 (which is 504) and we get a perfect square 5041 again!

j) Add 531441 and 254016 and the resultant number has factors 3,3,3,3 and a prime number 9697

k) Add 729 and 504 and the resultant number has factors 3,3 and a prime number 137! (see the pattern)

l) Subtract 531441 and 254016 and the resultant number has factors 3,3,3,3,5,5 and 137 again!

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