21704531 has 2 divisors, whose sum is σ = 21704532. Its totient is φ = 21704530.

The previous prime is 21704521. The next prime is 21704537. The reversal of 21704531 is 13540712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21704531 - 2⁶ = 21704467 is a prime.

It is a super-2 number, since 2×21704531² = 942173331859922, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21704497 and 21704506.

It is not a weakly prime, because it can be changed into another prime (21704537) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10852265 + 10852266.

It is an arithmetic number, because the mean of its divisors is an integer number (10852266).

Almost surely, 2^21704531 is an apocalyptic number.

21704531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21704531 is an equidigital number, since it uses as much as digits as its factorization.

21704531 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21704531 is about 4658.8121876719. The cubic root of 21704531 is about 278.9438571873.

The spelling of 21704531 in words is "twenty-one million, seven hundred four thousand, five hundred thirty-one".