the number av odd numbers in eech roe=1, 3, 5, 7,...=the odd numbers
thru roe 19, yu du 361 odd numbers...sum av first 19 odd numbers
so roe 20 start with the odd number 362
that odd num is 1+2*(n-1)=1+2*361=723
num numbers in roe 20=2*19+1=39
roe 20...723, 725, 727, 729, 731...
middel= 20 akrost & 20th tern av roe 20 is 761