21640731 has 8 divisors (see below), whose sum is σ = 32976384. Its totient is φ = 12366120.

The previous prime is 21640721. The next prime is 21640747. The reversal of 21640731 is 13704612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21640731 - 2⁶ = 21640667 is a prime.

It is a super-2 number, since 2×21640731² = 936642476428722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21640721) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 515235 + ... + 515276.

It is an arithmetic number, because the mean of its divisors is an integer number (4122048).

Almost surely, 2^21640731 is an apocalyptic number.

21640731 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21640731 is a deficient number, since it is larger than the sum of its proper divisors (11335653).

21640731 is a wasteful number, since it uses less digits than its factorization.

21640731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1030521.

The product of its (nonzero) digits is 1008, while the sum is 24.

The square root of 21640731 is about 4651.9599095435. The cubic root of 21640731 is about 278.6702724657.

The spelling of 21640731 in words is "twenty-one million, six hundred forty thousand, seven hundred thirty-one".