Answers

2015-11-28T13:22:53+05:30
Sum of first 20 numbers:-1*1+2*2+3*3+4*4+5*5+6*6+7*7+8*8+9*9+10*10+11*11+12*12+13*13+14*14+15*15+16*16+17*17+18*18+19*19+20*20
=2870
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2015-11-28T14:39:12+05:30
the sum of squares of the first 20 natural number is 2870.

hope so my answer is useful........^_^ 
1 5 1