I want a mathematical function (floor/ceiling etc. are fine but not piecewise) which does the following:
If the input is odd, just return that number i.e f(2n+1) = 2n+1
If the input is even return the odd number one less than it i.e f(2n) = 2n-1

I want a mathematical function (floor/ceiling etc. are fine but not piecewise) which does the following:
If the input is odd, just return that number i.e f(2n+1) = 2n+1
If the input is even return the odd number one less than it i.e f(2n) = 2n-1