Prove that a is a difference of consecutive cubes.
4a-1 is ODD and divisible by 3
We can assume 4a-1= 3*(2*k+1)^2=12*k^2+12*k+3
4*a=4*(3*k^2+3k+1)
a=3*k^2+3k+1= (k+1)^3-k^3 qed
Edited on March 25, 2017, 9:10 pm
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