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.

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?

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)