Natural numbers between 23 and 100 are 24, 25, ...99.
Natural numbers between 23 and 100 which are divisible by 6 are
24, 30, ...96.
In above A.P. first term a = 24, common difference (d) = 6
T(n) = a + (n-1)d
96 = 24 +(n-1) 6
(96-24)/6 + 1 = n
n = 13
Hence such numbers are 13.