49

is the integer between.

Math features

 * 49 is an odd number.
 * 49 is a composite number and a deficient number.
 * 49 is the first square number to have 2 square numbers concatenated. The second is 1444 with 144 and 4, and the third is 1601 with 16 and 1.
 * 49, being 50 - 1, plays an important part that ensures that 142857 is a cyclic number in base 10 (14, 28, 56, 98, 399 and 57 does too).
 * 49 is the first square number of the form $$x^2=2n^2-1$$ where n and x are any integer. Another square number like this is 57121, the square of 239 and 1681, the square of 41.