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And any number the any of the three forms will accure a multiple of three
like for n = 1 
1(1 +1)( 1 +5)
so we see 6 is a multiple of 3
again for even number 
n = 2
2(2 +1)(2+5)
so 3 is a multiple of three
so hence proved we take any number we get a multiple of 3