"Though an 'even''s seen in 'seven'..." What Are the Odds? An Anomoly of Numbers

Though an 'even''s seen in 'seven,' oddly, 7 isn't even.
That an 'even''s in 'eleven's odd: 11, too, ain't even.
An "An 'even''s seen in 'seven' although 7 isn't even"
seems, routinely, a fifteener. (Even so, 15 ain't even.)
An "An 'even''s in 'eleven' though 11 isn't even"
seems a byzantine fifteener. Still, 15 remains uneven.
(Note: these lines through which we plod
though, 'even's notwithstanding, odd,
we see wind down -- for which, thank God! --
and roundly boo'd as oddly flawed.)