21320531 has 2 divisors, whose sum is σ = 21320532. Its totient is φ = 21320530.

The previous prime is 21320513. The next prime is 21320543. The reversal of 21320531 is 13502312.

Together with previous prime (21320513) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21320531 - 2¹⁴ = 21304147 is a prime.

It is a super-2 number, since 2×21320531² = 909130084243922, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21320581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10660265 + 10660266.

It is an arithmetic number, because the mean of its divisors is an integer number (10660266).

Almost surely, 2^21320531 is an apocalyptic number.

21320531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21320531 is an equidigital number, since it uses as much as digits as its factorization.

21320531 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 180, while the sum is 17.

The square root of 21320531 is about 4617.4160522959. The cubic root of 21320531 is about 277.2890196253.

Adding to 21320531 its reverse (13502312), we get a palindrome (34822843).

The spelling of 21320531 in words is "twenty-one million, three hundred twenty thousand, five hundred thirty-one".