Symbols for "odd" and "even" Let $A$ be a sequence of letters $\langle a,b,c,d,e,f \rangle$. I want to create two subsequences, one with the values with odd index and other with the values with even index: $A_\mathrm{odd} = \langle a,c,e \rangle$ and $A_\mathrm{even} = \langle b,d,f \rangle$.
My question is: is there any usual symbol that could substitute the words "odd" and "even" in the name of the subsequence?
Thanks!

To say that $x$ is even is to say that $x\equiv 0 \bmod 2$ and to say that it is odd is to say that $x\equiv 1 \bmod 2$.  So you could use $A_0$ and $A_1$.
But, to be honest, I prefer $A_{\mathrm{e}}$ and $A_{\mathrm{o}}$, since they're as easy to remember as $A_{\mathrm{even}}$ and $A_{\mathrm{odd}}$ but more concise.
