Question 769841
The sum of the odd integers from 1 to 78
is {{{ ( 78/2 )^2 = 1521 }}}
The sum of the odd integers from 1 to 38
is {{{ ( 38/2 )^2 = 361 }}}
{{{ 1521 - 361 = 1160 }}}
This works for small sequences like
1,2,3,4,5,6,7,8 so I think it's right