21256731 has 24 divisors (see below), whose sum is σ = 32240000. Its totient is φ = 13478400.

The previous prime is 21256721. The next prime is 21256733. The reversal of 21256731 is 13765212.

It is a happy number.

It is not a de Polignac number, because 21256731 - 2²² = 17062427 is a prime.

It is a super-2 number, since 2×21256731² = 903697225612722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21256695 and 21256704.

It is not an unprimeable number, because it can be changed into a prime (21256733) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 16395 + ... + 17643.

Almost surely, 2^21256731 is an apocalyptic number.

21256731 is a deficient number, since it is larger than the sum of its proper divisors (10983269).

21256731 is a wasteful number, since it uses less digits than its factorization.

21256731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1347 (or 1344 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21256731 is about 4610.5022502977. The cubic root of 21256731 is about 277.0121548012.

The spelling of 21256731 in words is "twenty-one million, two hundred fifty-six thousand, seven hundred thirty-one".