21001731 has 4 divisors (see below), whose sum is σ = 28002312. Its totient is φ = 14001152.

The previous prime is 21001711. The next prime is 21001763. The reversal of 21001731 is 13710012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21001731 - 2⁶ = 21001667 is a prime.

It is a super-2 number, since 2×21001731² = 882145409992722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21001731.

It is not an unprimeable number, because it can be changed into a prime (21001711) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3500286 + ... + 3500291.

It is an arithmetic number, because the mean of its divisors is an integer number (7000578).

Almost surely, 2^21001731 is an apocalyptic number.

21001731 is a deficient number, since it is larger than the sum of its proper divisors (7000581).

21001731 is an equidigital number, since it uses as much as digits as its factorization.

21001731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7000580.

The product of its (nonzero) digits is 42, while the sum is 15.

The square root of 21001731 is about 4582.7645586480. The cubic root of 21001731 is about 275.8999979025.

Adding to 21001731 its reverse (13710012), we get a palindrome (34711743).

The spelling of 21001731 in words is "twenty-one million, one thousand, seven hundred thirty-one".