21609731 has 16 divisors (see below), whose sum is σ = 25519200. Its totient is φ = 18040320.

The previous prime is 21609713. The next prime is 21609733. The reversal of 21609731 is 13790612.

It is a cyclic number.

It is not a de Polignac number, because 21609731 - 2⁶ = 21609667 is a prime.

It is a super-2 number, since 2×21609731² = 933960947784722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21609694 and 21609703.

It is not an unprimeable number, because it can be changed into a prime (21609733) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 49691 + ... + 50123.

It is an arithmetic number, because the mean of its divisors is an integer number (1594950).

Almost surely, 2^21609731 is an apocalyptic number.

21609731 is a deficient number, since it is larger than the sum of its proper divisors (3909469).

21609731 is a wasteful number, since it uses less digits than its factorization.

21609731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 806.

The product of its (nonzero) digits is 2268, while the sum is 29.

The square root of 21609731 is about 4648.6267864822. The cubic root of 21609731 is about 278.5371453129.

The spelling of 21609731 in words is "twenty-one million, six hundred nine thousand, seven hundred thirty-one".