Adding to 123456 its reverse (654321), we get a palindrome (777777).
It is a happy number.
123456 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.
It is an Ulam number.
It is an alternating number because its digits alternate between odd and even.
It is a straight-line number, since its digits are in arithmetic progression.
It is a plaindrome in base 10.
2123456 is an apocalyptic number.
123456 is a gapful number since it is divisible by the number (16) formed by its first and last digit.
It is an amenable number.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
123456 is an equidigital number, since it uses as much as digits as its factorization.
123456 is an evil number, because the sum of its binary digits is even.
The square root of 123456 is about 351.3630600960. The cubic root of 123456 is about 49.7932798467.
The spelling of 123456 in words is "one hundred twenty-three thousand, four hundred fifty-six".