21065731 has 4 divisors (see below), whose sum is σ = 21090472. Its totient is φ = 21040992.

The previous prime is 21065711. The next prime is 21065741. The reversal of 21065731 is 13756012.

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 21065731 - 2¹⁷ = 20934659 is a prime.

It is a super-2 number, since 2×21065731² = 887530045128722, 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 = 21065696 and 21065705.

It is not an unprimeable number, because it can be changed into a prime (21065701) 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, 11046 + ... + 12811.

It is an arithmetic number, because the mean of its divisors is an integer number (5272618).

Almost surely, 2^21065731 is an apocalyptic number.

21065731 is a deficient number, since it is larger than the sum of its proper divisors (24741).

21065731 is an equidigital number, since it uses as much as digits as its factorization.

21065731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24740.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21065731 is about 4589.7419317430. The cubic root of 21065731 is about 276.1799699640.

The spelling of 21065731 in words is "twenty-one million, sixty-five thousand, seven hundred thirty-one".