Some conventions in typing math formula
  ^ is ** i.e 2^3 is 2**3 which is 8.

1. Subscripts and superscripts.
  x_i     is x with subscript   i   i.e.  x
                                           i

  x_{i+1} is x with subscript   i+1 i.e.  x       
                                           i+1

                                           i+1
  x^{i+1} is x with superscript i+1 i.e   x

                         2
  Similarly x_i^2 is    x
                         i

2. Logs
  lgn is base 2 logarithm of n
  logn depends on the context can be log_10 n or log_2 n mispelled.
  ln n is base e (e=2.7172...) logarithm of n
  log_a{n} is base a logarithm of n i.e. log_3{9} is 2 since 3^2 =9.

  lg{n} or \lg{n}  is lg(n)
  lg{n+1} or \lg{n+1} is lg(n+1)

  Similarly \lg^2{n} is \lg{n}*\lg{n} i.e. lgn squared.

3. Fractions.
  \frac{x}{y}  is x over y fraction i.e.   x
                                          ---
                                           y
  \frac{x^2+2x}{y_2^2} is a fraction with numerator x^2+2x
                       and denominator    y_2^2

4. Sums
  \sum_{i=1}^{n} i^2  is sum over i^2 which is i**2 (i squared)
   that starts from i=1 and ends for i=n. This sum is
   n(n+1)(2n+1)/6 which can be written as \frac{n(n+1)(2n+1)}{6}