(In reply to Answer
by K Sengupta)
Let the ith term of the given sequence be S(i).
Then, S(i) = smallest positive integer whose spelled out version
contain precisely (i+2) letters.
For example, the first term of the sequence is 1, which is spelled out as "one",which contains 3 letters. Therefore, S(1) = 3.
Similarly, S(2) = 4, since 4 is the smallest positive integer whose spelled out version contain precisely 4 letters.
We now observe that "twenty four" contains 10 letters and checking for the positive integers 1 to 24, we observe that 24 is indeed the smallest number with this property.
Thus, S(8) = 24
Similarly, checking for the numbers 1 to 23, we observe that the
word "twenty three" contains 11 letters, so that 23 is the smallest
positive integer with this property.
Therefore, S(9) = 23
Consequently, the required missing terms are 24 and 23.