Thanks for the Kata, finally got it. I didn't realize that we are allowed to alter the function definitions here at Codewars. I also think that this was a bit tough for 7 kyu, needed pen and paper + needed to learn new ways of writing python for this one, usually 7 kyu are pretty much tutorial stuff.

This is one of the basic Python golfing trick, you can find it on Internet quite easily.

No, this is not correct. You can squeeze out 4 characters more.

Am I correct in assuming that the code needs to start
"def sum_corners(n):return "
leaving just 9 characters for the code or the formula?

map() in python 2.x used to return a list, py3 it was changed so list(map(...)) must be used, see the solution replies for a better understanding

edit: basically it was solved in a previous py version

For python the #1 solution uses map() but it doesn't return an array as was asked... (?)

"yz" is not a palindrome. The string contains both "yz" and "zy", but they are not palindromes. "yzy" and "zyz" would be palindromes. (https://en.wikipedia.org/wiki/Palindrome)