If n is less than 1000000 then find the sum of
2+4+8+16+32+64+128+........+n

• Its clear that the given series is GP
  so a=2 & r=2 & n=?
  first find nth term,
  according to condition , 1000000> a*r^(n-1) => 1000000>2*2^(n-1)
  taking n= 20, we got 1000000> 1048576 which is not true
  so n should be less than 20, lets take n=19 now, 1000000 > 524288
  so n=19.
  now simply find sum of GP series where a=r=2 & n=19
  sum={2*(2^19-1)}/2-1
  sum= 1048574....
• 10 years agoHelpfull: Yes(0) No(0)
• It is in G.P. series where r=2 like (2^1+2^2+...)
  Let there r n term.
  So , 2^n=10^6
  => n=19.93
  we will take 19 .
  So the summation is {2.(2^19-1)}/(2-1)=1048574
• 10 years agoHelpfull: Yes(0) No(0)