511

is the integer between.

Math features

 * 511 is an odd number.
 * 511 is a composite number and a deficient number.
 * 511 is a Mersenne number, equal to 29 - 1.
 * 511 is a semiprime and an emirpimes, as 115, its palindrome, is also a semiprime.
 * 511 is a Harshad number, as it is a multiple of 5 + 1 + 1, which is 7.
 * 511 is a palindromic number in binary and octal.
 * 511 is a lucky number.