21004256 has 48 divisors (see below), whose sum is σ = 50901984. Its totient is φ = 8308224.

The previous prime is 21004241. The next prime is 21004261. The reversal of 21004256 is 65240012.

It is a happy number.

It is a super-2 number, since 2×21004256² = 882357540227072, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 695 + ... + 6518.

It is an arithmetic number, because the mean of its divisors is an integer number (1060458).

Almost surely, 2^21004256 is an apocalyptic number.

21004256 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

21004256 is an abundant number, since it is smaller than the sum of its proper divisors (29897728).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21004256 is a wasteful number, since it uses less digits than its factorization.

21004256 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7243 (or 7235 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 21004256 is about 4583.0400391007. The cubic root of 21004256 is about 275.9110544447.

Adding to 21004256 its reverse (65240012), we get a palindrome (86244268).

The spelling of 21004256 in words is "twenty-one million, four thousand, two hundred fifty-six".