Adding to 23456789 its reverse (98765432), we get a palindrome (122222221).
23456789 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.
It is a weak prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-23456789 is a prime.
It is a Chen prime.
It is an alternating number because its digits alternate between even and odd.
It is a straight-line number, since its digits are in arithmetic progression.
It is a plaindrome in base 10.
It is a congruent number.
Almost surely, 223456789 is an apocalyptic number.
It is an amenable number.
23456789 is an equidigital number, since it uses as much as digits as its factorization.
23456789 is an odious number, because the sum of its binary digits is odd.
The square root of 23456789 is about 4843.2209323961. The cubic root of 23456789 is about 286.2570471750.
The spelling of 23456789 in words is "twenty-three million, four hundred fifty-six thousand, seven hundred eighty-nine".